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[PATCH 0/8] schedutil enhancements

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  [PATCH 0/8] schedutil enhancements Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
    [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:30 +0100
        Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
          Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 04:40 +0100
            Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Peter Zijlstra <peterz@infradead.org> - 2016-03-16 09:10 +0100
              Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-16 11:10 +0100
                Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 19:00 +0100
                  Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:10 +0100
                  Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-17 10:40 +0100
                    Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Steve Muckle <steve.muckle@linaro.org> - 2016-03-17 15:00 +0100
                      Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Patrick Bellasi <patrick.bellasi@arm.com> - 2016-03-17 17:00 +0100
                        Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Juri Lelli <Juri.Lelli@arm.com> - 2016-03-17 19:00 +0100
                          Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-17 20:00 +0100
                            Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-17 23:40 +0100
              Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 13:50 +0100
            Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:10 +0100
    [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
        Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-15 23:00 +0100
      Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update() Peter Zijlstra <peterz@infradead.org> - 2016-03-16 09:10 +0100
    [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:30 +0100
        Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 05:00 +0100
        Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 08:50 +0100
          Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-16 09:40 +0100
            Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 10:00 +0100
              Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-16 10:20 +0100
              Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 13:40 +0100
                Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 14:20 +0100
                  Re: [PATCH 5/8] sched/cpufreq: pass sched class into cpufreq_update_util "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-16 14:30 +0100
                    Re: [PATCH 5/8] sched/cpufreq: pass sched class into  cpufreq_update_util Peter Zijlstra <peterz@infradead.org> - 2016-03-16 14:50 +0100
    [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-15 20:20 +0100
        Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Michael Turquette <mturquette@baylibre.com> - 2016-03-15 21:50 +0100
          Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-16 20:50 +0100
            Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 21:10 +0100
              Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-16 22:40 +0100
      Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
        Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 08:50 +0100
          Re: [PATCH 8/8] sched: prefer cpufreq_scale_freq_capacity Peter Zijlstra <peterz@infradead.org> - 2016-03-16 13:50 +0100
    [PATCH 2/8] sched/fair: add margin to utilization update Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 2/8] sched/fair: add margin to utilization update Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
        Re: [PATCH 2/8] sched/fair: add margin to utilization update Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:50 +0100
      Re: [PATCH 2/8] sched/fair: add margin to utilization update Steve Muckle <steve.muckle@linaro.org> - 2016-03-16 04:00 +0100
        Re: [PATCH 2/8] sched/fair: add margin to utilization update Michael Turquette <mturquette@baylibre.com> - 2016-03-16 23:20 +0100
    [PATCH 3/8] sched/cpufreq: new cfs capacity margin helpers Michael Turquette <mturquette@baylibre.com> - 2016-03-14 06:30 +0100
      Re: [PATCH 3/8] sched/cpufreq: new cfs capacity margin helpers Peter Zijlstra <peterz@infradead.org> - 2016-03-15 22:20 +0100
    Re: [PATCH 0/8] schedutil enhancements "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-16 01:10 +0100

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#1356939 — [PATCH 0/8] schedutil enhancements

I'm happy that scheduler-driven cpu frequency selection is getting some
attention. Rafael's recent schedutil governor is a step in the right direction.
This series builds on top of Rafael's schedutil governor, bringing it to parity
with some of the features in the schedfreq series posted by Steve[0], as well
as adding a couple of new things.

Patch 1 removes cpufreq_trigger_update()

Patches 2-4 move the cfs capacity margin out of the governor and into
cfs. This value is made tunable by a sysfs control in schedutil.

Patches 5-6 make cpufreq_update_util() aware of multiple scheduler
classes (cfs, rt & dl), and add storage & summation of these per-class
utilization values into schedutil.

Patches 7-8 introduces Dietmar's generic cpufreq implementation[1] of the
frequency invariance hook and changes the preprocessor magic in sched.h to
favor the cpufreq implementation over arch- or platform-specific ones.

If accepted, this series makes it trivial to port Steve and Juri's fine-grained
frequency selection in cfs and Vincent's rt utilization patch to the schedutil
governor.[2-6]

[0] lkml.kernel.org/r/1456190570-4475-1-git-send-email-smuckle@linaro.org
[1] https://git.linaro.org/people/steve.muckle/kernel.git/commit/1b7e57f89f14f7600e75e6fde42bf22d72927b3d
[2] lkml.kernel.org/r/1456190570-4475-5-git-send-email-smuckle@linaro.org
[3] lkml.kernel.org/r/1456190570-4475-6-git-send-email-smuckle@linaro.org
[4] lkml.kernel.org/r/1456190570-4475-7-git-send-email-smuckle@linaro.org
[5] lkml.kernel.org/r/1456190570-4475-8-git-send-email-smuckle@linaro.org
[6] lkml.kernel.org/r/1456190570-4475-11-git-send-email-smuckle@linaro.org

Dietmar Eggemann (1):
  cpufreq: Frequency invariant scheduler load-tracking support

Michael Turquette (7):
  sched/cpufreq: remove cpufreq_trigger_update()
  sched/fair: add margin to utilization update
  sched/cpufreq: new cfs capacity margin helpers
  cpufreq/schedutil: sysfs capacity margin tunable
  sched/cpufreq: pass sched class into cpufreq_update_util
  cpufreq/schedutil: sum per-sched class utilization
  sched: prefer cpufreq_scale_freq_capacity

 drivers/cpufreq/cpufreq.c           | 29 ++++++++++++
 drivers/cpufreq/cpufreq_governor.c  |  5 +-
 drivers/cpufreq/cpufreq_schedutil.c | 70 ++++++++++++++++++++++++----
 drivers/cpufreq/intel_pstate.c      |  5 +-
 include/linux/cpufreq.h             |  3 ++
 include/linux/sched.h               | 19 ++++++--
 kernel/sched/cpufreq.c              | 92 +++++++++++++++++++++++++------------
 kernel/sched/deadline.c             |  2 +-
 kernel/sched/fair.c                 | 18 +++++++-
 kernel/sched/rt.c                   |  2 +-
 kernel/sched/sched.h                | 29 +++++++++---
 11 files changed, 219 insertions(+), 55 deletions(-)

-- 
2.1.4

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#1356941 — [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

With the addition of the global cfs capacity margin helpers in patch,
"sched/cpufreq: new cfs capacity margin helpers", we can now export
sysfs tunables from the schedutil governor. This allows privileged users
to tune the value more easily.

The margin value is global to cfs, not per-policy. As such schedutil
does not store any state about the margin. Schedutil restores the margin
value to its default value when exiting.

Signed-off-by: Michael Turquette <mturquette+renesas@baylibre.com>
---
 drivers/cpufreq/cpufreq_schedutil.c | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/drivers/cpufreq/cpufreq_schedutil.c b/drivers/cpufreq/cpufreq_schedutil.c
index 5aa26bf..12e49b9 100644
--- a/drivers/cpufreq/cpufreq_schedutil.c
+++ b/drivers/cpufreq/cpufreq_schedutil.c
@@ -246,8 +246,32 @@ static ssize_t rate_limit_us_store(struct gov_attr_set *attr_set, const char *bu
 
 static struct governor_attr rate_limit_us = __ATTR_RW(rate_limit_us);
 
+static ssize_t capacity_margin_show(struct gov_attr_set *not_used,
+					   char *buf)
+{
+	return sprintf(buf, "%lu\n", cpufreq_get_cfs_capacity_margin());
+}
+
+static ssize_t capacity_margin_store(struct gov_attr_set *attr_set,
+				  const char *buf, size_t count)
+{
+	unsigned long margin;
+	int ret;
+
+	ret = sscanf(buf, "%lu", &margin);
+	if (ret != 1)
+		return -EINVAL;
+
+	cpufreq_set_cfs_capacity_margin(margin);
+
+	return count;
+}
+
+static struct governor_attr capacity_margin = __ATTR_RW(capacity_margin);
+
 static struct attribute *sugov_attributes[] = {
 	&rate_limit_us.attr,
+	&capacity_margin.attr,
 	NULL
 };
 
@@ -381,6 +405,7 @@ static int sugov_exit(struct cpufreq_policy *policy)
 
 	mutex_lock(&global_tunables_lock);
 
+	cpufreq_reset_cfs_capacity_margin();
 	count = gov_attr_set_put(&tunables->attr_set, &sg_policy->tunables_hook);
 	policy->governor_data = NULL;
 	if (!count)
-- 
2.1.4

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#1358253 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On Sun, Mar 13, 2016 at 10:22:08PM -0700, Michael Turquette wrote:
> With the addition of the global cfs capacity margin helpers in patch,
> "sched/cpufreq: new cfs capacity margin helpers", we can now export
> sysfs tunables from the schedutil governor. This allows privileged users
> to tune the value more easily.
> 
> The margin value is global to cfs, not per-policy. As such schedutil
> does not store any state about the margin. Schedutil restores the margin
> value to its default value when exiting.

Yuck sysfs.. I would really rather we did not expose this per default.
And certainly not in this weird form.

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#1358277 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On Tue, Mar 15, 2016 at 02:40:43PM -0700, Michael Turquette wrote:
> Quoting Peter Zijlstra (2016-03-15 14:20:47)
> > On Sun, Mar 13, 2016 at 10:22:08PM -0700, Michael Turquette wrote:
> > > With the addition of the global cfs capacity margin helpers in patch,
> > > "sched/cpufreq: new cfs capacity margin helpers", we can now export
> > > sysfs tunables from the schedutil governor. This allows privileged users
> > > to tune the value more easily.
> > > 
> > > The margin value is global to cfs, not per-policy. As such schedutil
> > > does not store any state about the margin. Schedutil restores the margin
> > > value to its default value when exiting.
> > 
> > Yuck sysfs.. I would really rather we did not expose this per default.
> > And certainly not in this weird form.
> 
> I'm happy to change capacity_margin to up_threshold and use a
> percentage.
> 
> The sysfs approach has two benefits. First, it is aligned with cpufreq
> user expectations. Second, there has been rough consensus that this
> value should be tunable and sysfs gets us there quickly and painlessly.
> We're already exporting rate_limit_us for schedutil via sysfs. Is there
> a better way interface you can recommend?

It really depends on how tunable you want this to be. Do we always want
this to be a tunable, or just now while we're playing about with the
whole thing?

The problem with exposing it in sysfs is that you cannot take it out
again, it becomes ABI.

What we do for all the scheduler tunables (pretty much every time we
have to take a value out of thin air), is we make them const for
!SCHED_DEBUG builds, but have them as sysctl for SCHED_DEBUG builds
(although we should probably move them to /debug/sched/ or somesuch).

That way you get better code generation (compile time constants rule)
for !debug builds, while having the 'joy' of poking at your number on
debug builds.

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#1358508 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 03/15/2016 03:37 PM, Michael Turquette wrote:
>>>> Yuck sysfs.. I would really rather we did not expose this per default.
>>>> > > > And certainly not in this weird form.
>>> > > 
>>> > > I'm happy to change capacity_margin to up_threshold and use a
>>> > > percentage.
>>> > > 
>>> > > The sysfs approach has two benefits. First, it is aligned with cpufreq
>>> > > user expectations. Second, there has been rough consensus that this
>>> > > value should be tunable and sysfs gets us there quickly and painlessly.
>>> > > We're already exporting rate_limit_us for schedutil via sysfs. Is there
>>> > > a better way interface you can recommend?
>> > 
>> > It really depends on how tunable you want this to be. Do we always want
>> > this to be a tunable, or just now while we're playing about with the
>> > whole thing?
>
> I had considered this myself, and I really think that Steve and Juri
> should chime in as they have spent more time tuning and running the
> numbers.
> 
> I'm inclined to think that a debug version would be good enough, as I
> don't imagine this value being changed at run-time by some userspace
> daemon or something.
> 
> Then again, maybe this knob will be part of the mythical
> power-vs-performance slider?

Patrick Bellasi's schedtune series [0] (which I think is the referenced
mythical slider) aims to provide a more sophisticated interface for
tuning scheduler-driven frequency selection. In addition to a global
boost value it includes a cgroup controller as well for per-task tuning.

I would definitely expect the margin/boost value to be modified at
runtime, for example if the battery is running low, or the user wants
100% performance for a while, or the userspace framework wants to
temporarily tailor the performance level for a particular set of tasks, etc.

[0] http://article.gmane.org/gmane.linux.kernel/2022959

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#1358612 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> > Then again, maybe this knob will be part of the mythical
> > power-vs-performance slider?
> 
> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> mythical slider) aims to provide a more sophisticated interface for
> tuning scheduler-driven frequency selection. In addition to a global
> boost value it includes a cgroup controller as well for per-task tuning.
> 
> I would definitely expect the margin/boost value to be modified at
> runtime, for example if the battery is running low, or the user wants
> 100% performance for a while, or the userspace framework wants to
> temporarily tailor the performance level for a particular set of tasks, etc.

OK, so how about we start with it as a debug knob, and once we have
experience and feel like it is indeed a useful runtime knob, we upgrade
it to ABI.

The problem with starting out as ABI is that its hard to take away
again.

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#1358782 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

Hi,

On 16/03/16 09:05, Peter Zijlstra wrote:
> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> > > Then again, maybe this knob will be part of the mythical
> > > power-vs-performance slider?
> > 
> > Patrick Bellasi's schedtune series [0] (which I think is the referenced
> > mythical slider) aims to provide a more sophisticated interface for
> > tuning scheduler-driven frequency selection. In addition to a global
> > boost value it includes a cgroup controller as well for per-task tuning.
> > 
> > I would definitely expect the margin/boost value to be modified at
> > runtime, for example if the battery is running low, or the user wants
> > 100% performance for a while, or the userspace framework wants to
> > temporarily tailor the performance level for a particular set of tasks, etc.
> 
> OK, so how about we start with it as a debug knob, and once we have
> experience and feel like it is indeed a useful runtime knob, we upgrade
> it to ABI.
> 

I tend to agree here. To me the margin is something that we need to make
this thing work and to get acceptable performance out of the box. So we
can play with it while debugging, but I consider the schedtune slider as
the way to tune the system at runtime.

Best,

- Juri

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#1359208 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 03/16/2016 03:02 AM, Juri Lelli wrote:
> Hi,
> 
> On 16/03/16 09:05, Peter Zijlstra wrote:
>> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
>>>> Then again, maybe this knob will be part of the mythical
>>>> power-vs-performance slider?
>>>
>>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
>>> mythical slider) aims to provide a more sophisticated interface for
>>> tuning scheduler-driven frequency selection. In addition to a global
>>> boost value it includes a cgroup controller as well for per-task tuning.
>>>
>>> I would definitely expect the margin/boost value to be modified at
>>> runtime, for example if the battery is running low, or the user wants
>>> 100% performance for a while, or the userspace framework wants to
>>> temporarily tailor the performance level for a particular set of tasks, etc.
>>
>> OK, so how about we start with it as a debug knob, and once we have
>> experience and feel like it is indeed a useful runtime knob, we upgrade
>> it to ABI.
>>
> 
> I tend to agree here. To me the margin is something that we need to make
> this thing work and to get acceptable performance out of the box. So we
> can play with it while debugging, but I consider the schedtune slider as
> the way to tune the system at runtime.

Could the default schedtune value not serve as the out of the box margin?

Regardless I agree that a debug interface is the way to go for now while
we figure things out.

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#1359386 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

Quoting Steve Muckle (2016-03-16 10:55:49)
> On 03/16/2016 03:02 AM, Juri Lelli wrote:
> > Hi,
> > 
> > On 16/03/16 09:05, Peter Zijlstra wrote:
> >> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> >>>> Then again, maybe this knob will be part of the mythical
> >>>> power-vs-performance slider?
> >>>
> >>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> >>> mythical slider) aims to provide a more sophisticated interface for
> >>> tuning scheduler-driven frequency selection. In addition to a global
> >>> boost value it includes a cgroup controller as well for per-task tuning.
> >>>
> >>> I would definitely expect the margin/boost value to be modified at
> >>> runtime, for example if the battery is running low, or the user wants
> >>> 100% performance for a while, or the userspace framework wants to
> >>> temporarily tailor the performance level for a particular set of tasks, etc.
> >>
> >> OK, so how about we start with it as a debug knob, and once we have
> >> experience and feel like it is indeed a useful runtime knob, we upgrade
> >> it to ABI.
> >>
> > 
> > I tend to agree here. To me the margin is something that we need to make
> > this thing work and to get acceptable performance out of the box. So we
> > can play with it while debugging, but I consider the schedtune slider as
> > the way to tune the system at runtime.
> 
> Could the default schedtune value not serve as the out of the box margin?

It can. Let's keep the kernel interfaces in patch #2 for changing the
margin/threshold, and schedtune can call these interfaces.

Regards,
Mike

> 
> Regardless I agree that a debug interface is the way to go for now while
> we figure things out.
> 

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#1359666 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 16/03/16 10:55, Steve Muckle wrote:
> On 03/16/2016 03:02 AM, Juri Lelli wrote:
> > Hi,
> > 
> > On 16/03/16 09:05, Peter Zijlstra wrote:
> >> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
> >>>> Then again, maybe this knob will be part of the mythical
> >>>> power-vs-performance slider?
> >>>
> >>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> >>> mythical slider) aims to provide a more sophisticated interface for
> >>> tuning scheduler-driven frequency selection. In addition to a global
> >>> boost value it includes a cgroup controller as well for per-task tuning.
> >>>
> >>> I would definitely expect the margin/boost value to be modified at
> >>> runtime, for example if the battery is running low, or the user wants
> >>> 100% performance for a while, or the userspace framework wants to
> >>> temporarily tailor the performance level for a particular set of tasks, etc.
> >>
> >> OK, so how about we start with it as a debug knob, and once we have
> >> experience and feel like it is indeed a useful runtime knob, we upgrade
> >> it to ABI.
> >>
> > 
> > I tend to agree here. To me the margin is something that we need to make
> > this thing work and to get acceptable performance out of the box. So we
> > can play with it while debugging, but I consider the schedtune slider as
> > the way to tune the system at runtime.
> 
> Could the default schedtune value not serve as the out of the box margin?
> 

I'm not sure I understand you here. For me schedtune should be disabled
by default, so I'd say that it doesn't introduce any additional margin
by default. But we still need a margin to make the governor work without
schedtune in the mix.

> Regardless I agree that a debug interface is the way to go for now while
> we figure things out.
> 

Looks good to me.

Best,

- Juri

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#1359870 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 03/17/2016 02:40 AM, Juri Lelli wrote:
>> Could the default schedtune value not serve as the out of the box margin?
>>
> I'm not sure I understand you here. For me schedtune should be disabled
> by default, so I'd say that it doesn't introduce any additional margin
> by default. But we still need a margin to make the governor work without
> schedtune in the mix.

Why not have schedtune be enabled always, and use it to add the margin?
It seems like it'd simplify things.

I haven't looked at the schedtune code at all so I don't know whether
this makes sense given its current implementation. But conceptually I
don't know why we'd need or want one margin in schedutil which will be
tunable, and then another mechanism for tuning as well.

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#1359973 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On 17-Mar 06:55, Steve Muckle wrote:
> On 03/17/2016 02:40 AM, Juri Lelli wrote:
> >> Could the default schedtune value not serve as the out of the box margin?
> >>
> > I'm not sure I understand you here. For me schedtune should be disabled
> > by default, so I'd say that it doesn't introduce any additional margin
> > by default. But we still need a margin to make the governor work without
> > schedtune in the mix.
> 
> Why not have schedtune be enabled always, and use it to add the margin?
> It seems like it'd simplify things.

Actually one of the effects we noticed when SchedTune and SchedFreq
are both in use is that we have a sort of "double boosting" effect.

SchedTune boosts the CPU utilization signal, thus already providing a
sort of margin for the selection of the OPP. This margin overlaps with
the SchedFreq margin, which in turns could results in the selection of
an OPP even more higher than required (with boost already accouned).
 
> I haven't looked at the schedtune code at all so I don't know whether
> this makes sense given its current implementation.

The current implementation requires review, of course ;-)
Last (and only) posting is based on top of SchedFreq code, as it was
at that time.

> But conceptually I don't know why we'd need or want one margin in
> schedutil which will be tunable, and then another mechanism for
> tuning as well.

I agree with Steve on the conceptual standpoint. The main goal of
SchedTune is actually to provide a "single tunable" to bias many
different subsystem in a "consistent" way. Thus, from a conceptual
standpoint, IMO it makes sens to investigate better how the boost value
can be linked with SchedFreq.

A possible option can be to:
1. use an hardcoded margin (M) defined by SchedFreq
   this margin is used to trigger OPP jumps
   when SchedTune _is not_ in use
2. "compose" the M margin with a boost value defined margin (B)
   when SchedTune _is_ in use

This means, e.g.
  schedfreq_margin = max(M, B)
Thus:
a) non boosted tasks (and in general when SchedTune is not in use)
   gets OPPs jumps based on the hardcoded M margin
b) boosted tasks can get more aggressive OPPs jumps based on the B
   margin

While the M margin is hardcoded, the B one is defined via CGroups
depending on the how much tasks needs to be boosted.

-- 
#include <best/regards.h>

Patrick Bellasi

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#1360097 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

Hi,

On 17/03/16 15:53, Patrick Bellasi wrote:
> On 17-Mar 06:55, Steve Muckle wrote:
> > On 03/17/2016 02:40 AM, Juri Lelli wrote:
> > >> Could the default schedtune value not serve as the out of the box margin?
> > >>
> > > I'm not sure I understand you here. For me schedtune should be disabled
> > > by default, so I'd say that it doesn't introduce any additional margin
> > > by default. But we still need a margin to make the governor work without
> > > schedtune in the mix.
> > 
> > Why not have schedtune be enabled always, and use it to add the margin?
> > It seems like it'd simplify things.
> 
> Actually one of the effects we noticed when SchedTune and SchedFreq
> are both in use is that we have a sort of "double boosting" effect.
> 
> SchedTune boosts the CPU utilization signal, thus already providing a
> sort of margin for the selection of the OPP. This margin overlaps with
> the SchedFreq margin, which in turns could results in the selection of
> an OPP even more higher than required (with boost already accouned).
>  
> > I haven't looked at the schedtune code at all so I don't know whether
> > this makes sense given its current implementation.
> 
> The current implementation requires review, of course ;-)
> Last (and only) posting is based on top of SchedFreq code, as it was
> at that time.
> 
> > But conceptually I don't know why we'd need or want one margin in
> > schedutil which will be tunable, and then another mechanism for
> > tuning as well.
> 
> I agree with Steve on the conceptual standpoint. The main goal of
> SchedTune is actually to provide a "single tunable" to bias many
> different subsystem in a "consistent" way. Thus, from a conceptual
> standpoint, IMO it makes sens to investigate better how the boost value
> can be linked with SchedFreq.
> 
> A possible option can be to:
> 1. use an hardcoded margin (M) defined by SchedFreq
>    this margin is used to trigger OPP jumps
>    when SchedTune _is not_ in use
> 2. "compose" the M margin with a boost value defined margin (B)
>    when SchedTune _is_ in use
> 
> This means, e.g.
>   schedfreq_margin = max(M, B)
> Thus:
> a) non boosted tasks (and in general when SchedTune is not in use)
>    gets OPPs jumps based on the hardcoded M margin
> b) boosted tasks can get more aggressive OPPs jumps based on the B
>    margin
> 
> While the M margin is hardcoded, the B one is defined via CGroups
> depending on the how much tasks needs to be boosted.
> 

Makes sense to me. And I think M margin is the one we don't want to make
part of the ABI and only play with it under DEBUG.

Best,

- Juri

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#1360136 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

Quoting Juri Lelli (2016-03-17 10:54:07)
> Hi,
> 
> On 17/03/16 15:53, Patrick Bellasi wrote:
> > On 17-Mar 06:55, Steve Muckle wrote:
> > > On 03/17/2016 02:40 AM, Juri Lelli wrote:
> > > >> Could the default schedtune value not serve as the out of the box margin?
> > > >>
> > > > I'm not sure I understand you here. For me schedtune should be disabled
> > > > by default, so I'd say that it doesn't introduce any additional margin
> > > > by default. But we still need a margin to make the governor work without
> > > > schedtune in the mix.
> > > 
> > > Why not have schedtune be enabled always, and use it to add the margin?
> > > It seems like it'd simplify things.
> > 
> > Actually one of the effects we noticed when SchedTune and SchedFreq
> > are both in use is that we have a sort of "double boosting" effect.
> > 
> > SchedTune boosts the CPU utilization signal, thus already providing a
> > sort of margin for the selection of the OPP. This margin overlaps with
> > the SchedFreq margin, which in turns could results in the selection of
> > an OPP even more higher than required (with boost already accouned).
> >  
> > > I haven't looked at the schedtune code at all so I don't know whether
> > > this makes sense given its current implementation.
> > 
> > The current implementation requires review, of course ;-)
> > Last (and only) posting is based on top of SchedFreq code, as it was
> > at that time.
> > 
> > > But conceptually I don't know why we'd need or want one margin in
> > > schedutil which will be tunable, and then another mechanism for
> > > tuning as well.
> > 
> > I agree with Steve on the conceptual standpoint. The main goal of
> > SchedTune is actually to provide a "single tunable" to bias many
> > different subsystem in a "consistent" way. Thus, from a conceptual
> > standpoint, IMO it makes sens to investigate better how the boost value
> > can be linked with SchedFreq.
> > 
> > A possible option can be to:
> > 1. use an hardcoded margin (M) defined by SchedFreq
> >    this margin is used to trigger OPP jumps
> >    when SchedTune _is not_ in use
> > 2. "compose" the M margin with a boost value defined margin (B)
> >    when SchedTune _is_ in use
> > 
> > This means, e.g.
> >   schedfreq_margin = max(M, B)
> > Thus:
> > a) non boosted tasks (and in general when SchedTune is not in use)
> >    gets OPPs jumps based on the hardcoded M margin
> > b) boosted tasks can get more aggressive OPPs jumps based on the B
> >    margin
> > 
> > While the M margin is hardcoded, the B one is defined via CGroups
> > depending on the how much tasks needs to be boosted.
> > 
> 
> Makes sense to me. And I think M margin is the one we don't want to make
> part of the ABI and only play with it under DEBUG.

Correct.

Regarding "composing" the margin, schedtune could even overwrite the
margin entirely via cpufreq_set_cfs_capacity_margin (see patch #2 in
this series). This avoids complications around a "double boosting"
effect.

Either way, it sounds like the schedtune angle is something that we can
figure out in due time and change the code as needed later on. For
schedutil to make sense for frequency-invariant platforms we do need a
margin today, and there is desire to tune it easily, so I will move this
sysfs knob to a debug knob in v2.

Regards,
Mike

> 
> Best,
> 
> - Juri

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#1360238 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On Thu, Mar 17, 2016 at 7:56 PM, Michael Turquette
<mturquette@baylibre.com> wrote:
> Quoting Juri Lelli (2016-03-17 10:54:07)
>> Hi,
>>
>> On 17/03/16 15:53, Patrick Bellasi wrote:
>> > On 17-Mar 06:55, Steve Muckle wrote:
>> > > On 03/17/2016 02:40 AM, Juri Lelli wrote:
>> > > >> Could the default schedtune value not serve as the out of the box margin?
>> > > >>
>> > > > I'm not sure I understand you here. For me schedtune should be disabled
>> > > > by default, so I'd say that it doesn't introduce any additional margin
>> > > > by default. But we still need a margin to make the governor work without
>> > > > schedtune in the mix.
>> > >
>> > > Why not have schedtune be enabled always, and use it to add the margin?
>> > > It seems like it'd simplify things.
>> >
>> > Actually one of the effects we noticed when SchedTune and SchedFreq
>> > are both in use is that we have a sort of "double boosting" effect.
>> >
>> > SchedTune boosts the CPU utilization signal, thus already providing a
>> > sort of margin for the selection of the OPP. This margin overlaps with
>> > the SchedFreq margin, which in turns could results in the selection of
>> > an OPP even more higher than required (with boost already accouned).
>> >
>> > > I haven't looked at the schedtune code at all so I don't know whether
>> > > this makes sense given its current implementation.
>> >
>> > The current implementation requires review, of course ;-)
>> > Last (and only) posting is based on top of SchedFreq code, as it was
>> > at that time.
>> >
>> > > But conceptually I don't know why we'd need or want one margin in
>> > > schedutil which will be tunable, and then another mechanism for
>> > > tuning as well.
>> >
>> > I agree with Steve on the conceptual standpoint. The main goal of
>> > SchedTune is actually to provide a "single tunable" to bias many
>> > different subsystem in a "consistent" way. Thus, from a conceptual
>> > standpoint, IMO it makes sens to investigate better how the boost value
>> > can be linked with SchedFreq.
>> >
>> > A possible option can be to:
>> > 1. use an hardcoded margin (M) defined by SchedFreq
>> >    this margin is used to trigger OPP jumps
>> >    when SchedTune _is not_ in use
>> > 2. "compose" the M margin with a boost value defined margin (B)
>> >    when SchedTune _is_ in use
>> >
>> > This means, e.g.
>> >   schedfreq_margin = max(M, B)
>> > Thus:
>> > a) non boosted tasks (and in general when SchedTune is not in use)
>> >    gets OPPs jumps based on the hardcoded M margin
>> > b) boosted tasks can get more aggressive OPPs jumps based on the B
>> >    margin
>> >
>> > While the M margin is hardcoded, the B one is defined via CGroups
>> > depending on the how much tasks needs to be boosted.
>> >
>>
>> Makes sense to me. And I think M margin is the one we don't want to make
>> part of the ABI and only play with it under DEBUG.
>
> Correct.
>
> Regarding "composing" the margin, schedtune could even overwrite the
> margin entirely via cpufreq_set_cfs_capacity_margin (see patch #2 in
> this series). This avoids complications around a "double boosting"
> effect.
>
> Either way, it sounds like the schedtune angle is something that we can
> figure out in due time and change the code as needed later on. For
> schedutil to make sense for frequency-invariant platforms we do need a
> margin today, and there is desire to tune it easily, so I will move this
> sysfs knob to a debug knob in v2.

Sounds good!

Also, if you look at the latest iteration of the schedutil patch
(https://patchwork.kernel.org/patch/8612561/), it maps the choice of
the margin to the choice of the frequency tipping point.  That is, the
value of (util / max) for which the frequency will stay the same as it
was before.  [For (util / max) below the tipping point the new
frequency will be less than the old one (unless it already is minimum)
and for (util / max) above it, the new frequency will be greater than
the old one.]

The tipping point seems to be a good candidate for a tunable to me,
because its meaning is well defined and the range of values that make
sense is quite easy to figure out too.

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#1358956 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

On Wed, Mar 16, 2016 at 9:05 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Tue, Mar 15, 2016 at 08:36:57PM -0700, Steve Muckle wrote:
>> > Then again, maybe this knob will be part of the mythical
>> > power-vs-performance slider?
>>
>> Patrick Bellasi's schedtune series [0] (which I think is the referenced
>> mythical slider) aims to provide a more sophisticated interface for
>> tuning scheduler-driven frequency selection. In addition to a global
>> boost value it includes a cgroup controller as well for per-task tuning.
>>
>> I would definitely expect the margin/boost value to be modified at
>> runtime, for example if the battery is running low, or the user wants
>> 100% performance for a while, or the userspace framework wants to
>> temporarily tailor the performance level for a particular set of tasks, etc.
>
> OK, so how about we start with it as a debug knob, and once we have
> experience and feel like it is indeed a useful runtime knob, we upgrade
> it to ABI.
>
> The problem with starting out as ABI is that its hard to take away
> again.

Agreed, plus it is quite hard to get ABI right from the outset.  Even
if we decide on a sysfs knob, it still is unclear what exactly should
be represented by it in what units etc.

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#1359390 — Re: [PATCH 4/8] cpufreq/schedutil: sysfs capacity margin tunable

Quoting Steve Muckle (2016-03-15 20:36:57)
> On 03/15/2016 03:37 PM, Michael Turquette wrote:
> >>>> Yuck sysfs.. I would really rather we did not expose this per default.
> >>>> > > > And certainly not in this weird form.
> >>> > > 
> >>> > > I'm happy to change capacity_margin to up_threshold and use a
> >>> > > percentage.
> >>> > > 
> >>> > > The sysfs approach has two benefits. First, it is aligned with cpufreq
> >>> > > user expectations. Second, there has been rough consensus that this
> >>> > > value should be tunable and sysfs gets us there quickly and painlessly.
> >>> > > We're already exporting rate_limit_us for schedutil via sysfs. Is there
> >>> > > a better way interface you can recommend?
> >> > 
> >> > It really depends on how tunable you want this to be. Do we always want
> >> > this to be a tunable, or just now while we're playing about with the
> >> > whole thing?
> >
> > I had considered this myself, and I really think that Steve and Juri
> > should chime in as they have spent more time tuning and running the
> > numbers.
> > 
> > I'm inclined to think that a debug version would be good enough, as I
> > don't imagine this value being changed at run-time by some userspace
> > daemon or something.
> > 
> > Then again, maybe this knob will be part of the mythical
> > power-vs-performance slider?
> 
> Patrick Bellasi's schedtune series [0] (which I think is the referenced
> mythical slider) aims to provide a more sophisticated interface for
> tuning scheduler-driven frequency selection. In addition to a global
> boost value it includes a cgroup controller as well for per-task tuning.

/me spends 15 seconds looking schedtune

> 
> I would definitely expect the margin/boost value to be modified at
> runtime, for example if the battery is running low, or the user wants
> 100% performance for a while, or the userspace framework wants to
> temporarily tailor the performance level for a particular set of tasks, etc.

Right, and it looks like schedtune is a kernel solution, not userspace
solution. The following three interfaces from patch #2 could be used by
schedtune:

unsigned long cpufreq_get_cfs_capacity_margin(void);
void cpufreq_set_cfs_capacity_margin(unsigned long margin);
void cpufreq_reset_cfs_capacity_margin(void);

Then we can let schedtune worry about the userspace abi.

So I'll keep the basic idea of this patch, but explore making it
debuggy, instead of sysfsy.

Regards,
Mike

> 
> [0] http://article.gmane.org/gmane.linux.kernel/2022959

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#1356943 — [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update()

cpufreq_trigger_update() was introduced in "cpufreq: Rework the
scheduler hooks for triggering updates"[0]. Consensus is that this
helper is not needed and removing it will aid in experimenting with
deadline and rt capacity requests.

Instead of reverting the above patch, which includes useful renaming of
data structures and related functions, simply remove the function,
update affected kerneldoc and change rt.c and deadline.c to use
cpufreq_update_util().

[0] lkml.kernel.org/r/7541372.ciUW4go8Ux@vostro.rjw.lan

Signed-off-by: Michael Turquette <mturquette+renesas@baylibre.com>
---
 kernel/sched/cpufreq.c  | 28 ++--------------------------
 kernel/sched/deadline.c |  2 +-
 kernel/sched/rt.c       |  2 +-
 kernel/sched/sched.h    |  2 --
 4 files changed, 4 insertions(+), 30 deletions(-)

diff --git a/kernel/sched/cpufreq.c b/kernel/sched/cpufreq.c
index eecaba4..bd012c2 100644
--- a/kernel/sched/cpufreq.c
+++ b/kernel/sched/cpufreq.c
@@ -20,8 +20,8 @@ static DEFINE_PER_CPU(struct freq_update_hook *, cpufreq_freq_update_hook);
  *
  * Set and publish the freq_update_hook pointer for the given CPU.  That pointer
  * points to a struct freq_update_hook object containing a callback function
- * to call from cpufreq_trigger_update().  That function will be called from
- * an RCU read-side critical section, so it must not sleep.
+ * to call from cpufreq_update_util().  That function will be called from an
+ * RCU read-side critical section, so it must not sleep.
  *
  * Callers must use RCU-sched callbacks to free any memory that might be
  * accessed via the old update_util_data pointer or invoke synchronize_sched()
@@ -87,27 +87,3 @@ void cpufreq_update_util(u64 time, unsigned long util, unsigned long max)
 	if (hook)
 		hook->func(hook, time, util, max);
 }
-
-/**
- * cpufreq_trigger_update - Trigger CPU performance state evaluation if needed.
- * @time: Current time.
- *
- * The way cpufreq is currently arranged requires it to evaluate the CPU
- * performance state (frequency/voltage) on a regular basis.  To facilitate
- * that, cpufreq_update_util() is called by update_load_avg() in CFS when
- * executed for the current CPU's runqueue.
- *
- * However, this isn't sufficient to prevent the CPU from being stuck in a
- * completely inadequate performance level for too long, because the calls
- * from CFS will not be made if RT or deadline tasks are active all the time
- * (or there are RT and DL tasks only).
- *
- * As a workaround for that issue, this function is called by the RT and DL
- * sched classes to trigger extra cpufreq updates to prevent it from stalling,
- * but that really is a band-aid.  Going forward it should be replaced with
- * solutions targeted more specifically at RT and DL tasks.
- */
-void cpufreq_trigger_update(u64 time)
-{
-	cpufreq_update_util(time, ULONG_MAX, 0);
-}
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 1a035fa..3fd5bc4 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -728,7 +728,7 @@ static void update_curr_dl(struct rq *rq)
 
 	/* Kick cpufreq (see the comment in drivers/cpufreq/cpufreq.c). */
 	if (cpu_of(rq) == smp_processor_id())
-		cpufreq_trigger_update(rq_clock(rq));
+		cpufreq_update_util(rq_clock(rq), ULONG_MAX, 0);
 
 	/*
 	 * Consumed budget is computed considering the time as
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 9dd1c09..53ad077 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -947,7 +947,7 @@ static void update_curr_rt(struct rq *rq)
 
 	/* Kick cpufreq (see the comment in drivers/cpufreq/cpufreq.c). */
 	if (cpu_of(rq) == smp_processor_id())
-		cpufreq_trigger_update(rq_clock(rq));
+		cpufreq_update_util(rq_clock(rq), ULONG_MAX, 0);
 
 	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
 	if (unlikely((s64)delta_exec <= 0))
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 7ae012e..f06dfca 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1742,9 +1742,7 @@ static inline u64 irq_time_read(int cpu)
 
 #ifdef CONFIG_CPU_FREQ
 void cpufreq_update_util(u64 time, unsigned long util, unsigned long max);
-void cpufreq_trigger_update(u64 time);
 #else
 static inline void cpufreq_update_util(u64 time, unsigned long util,
 				       unsigned long max) {}
-static inline void cpufreq_trigger_update(u64 time) {}
 #endif /* CONFIG_CPU_FREQ */
-- 
2.1.4

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#1358250 — Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update()

On Sun, Mar 13, 2016 at 10:22:05PM -0700, Michael Turquette wrote:
> cpufreq_trigger_update() was introduced in "cpufreq: Rework the
> scheduler hooks for triggering updates"[0]. Consensus is that this
> helper is not needed and removing it will aid in experimenting with
> deadline and rt capacity requests.
> 
> Instead of reverting the above patch, which includes useful renaming of
> data structures and related functions, simply remove the function,
> update affected kerneldoc and change rt.c and deadline.c to use
> cpufreq_update_util().

This fails to explain how the need for these hooks is dealt with.

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#1358283 — Re: [PATCH 1/8] sched/cpufreq: remove cpufreq_trigger_update()

On Tue, Mar 15, 2016 at 02:45:45PM -0700, Michael Turquette wrote:
> Quoting Peter Zijlstra (2016-03-15 14:14:48)
> > On Sun, Mar 13, 2016 at 10:22:05PM -0700, Michael Turquette wrote:
> > > cpufreq_trigger_update() was introduced in "cpufreq: Rework the
> > > scheduler hooks for triggering updates"[0]. Consensus is that this
> > > helper is not needed and removing it will aid in experimenting with
> > > deadline and rt capacity requests.
> > > 
> > > Instead of reverting the above patch, which includes useful renaming of
> > > data structures and related functions, simply remove the function,
> > > update affected kerneldoc and change rt.c and deadline.c to use
> > > cpufreq_update_util().
> > 
> > This fails to explain how the need for these hooks is dealt with.
> 
> Sorry, I don't understand your point. The removed hook,
> "cpufreq_trigger_update()" was only used in deadline.c and rt.c, and
> this patch effectively reverts Rafael's patch that introduces that
> function.
> 
> It simply does not revert the other changes in Rafael's patch, such as
> some renaming.
> 
> deadline.c and rt.c are made to use cpufreq_update_util() and pass in
> ULONG_MAX for capacity and 0 for time. This is exactly what they did
> before patch "cpufreq: Rework the scheduler hooks for triggering
> updates".

Clearly I need to learn to read again.. You're right.

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