[PATCH 0/6] cpufreq: schedutil governor

From	"Rafael J. Wysocki" <rjw@rjwysocki.net>
Newsgroups	linux.kernel
Subject	[PATCH 0/6] cpufreq: schedutil governor
Date	2016-03-02 03:30 +0100
Message-ID	<r84I2-18B-15@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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Hi,

My previous intro message still applies somewhat, so here's a link:

http://marc.info/?l=linux-pm&m=145609673008122&w=2

The executive summary of the motivation is that I wanted to do two things:
use the utilization data from the scheduler (it's passed to the governor
as aguments of update callbacks anyway) and make it possible to set
CPU frequency without involving process context (fast frequency switching).

Both have been prototyped in the previous RFCs:

https://patchwork.kernel.org/patch/8426691/
https://patchwork.kernel.org/patch/8426741/

but in the meantime I found a couple of issues in there.

First off, the common governor code relied on by the previous version reset
the sample delay to 0 in order to force an immediate frequency update.  That
doesn't work with the new governor, though, because it computes the frequency
to set in a cpufreq_update_util() callback and (when fast switching is not
used) passes that to a work item which sets the frequency and then restores
the sample delay.  Thus if sysfs changes the sample delay to 0 when work_in_progress
is in effect, it will be overwritten by the work item and so discarded.

When using fast switching, the previous version would update the sample delay
from a scheduler path, but that (on a 32-bit system) might clash with an
update from sysfs leading to a result that's completely off.  That value would
be less than the correct sample delay (I think), so in practice that shouldn't
matter that much, but still it's not nice.

The above means that schedutil cannot really share as much code as I thought it
could with "ondemand" and "conservative".

Moreover, I wanted to have a "rate_limit" tunable (instead of the sampling rate
which doesn't mean what the name suggests in schedutil), but that would be the
only one used by schedutil, so I ended up having to define a new struct to point
to from struct dbs_data just to hold that single value and I would need to
define ->init() and ->exit() callbacks for the governor for that reason (and
the common tunables in struct dbs_data wouldn't be used).

Not to mention the fact that the majority of the common governor code is not
really used by schedutil anyway.

Taking the above into account, I decided to decouple schedutil from the other
governors, but I wanted to avoid duplicating some of the tunables manipulation
code.  Hence patches [3-4/6] taking that code into a separate file so schedutil
can use it too without pulling the rest of the common "ondemand" and
"conservative" code along with it.

Patch [5/6] adds support for fast switching to the core and the ACPI driver,
but doesn't hook it up to anything useful.  That is done in the last patch
that actually adds the new governor.

That depends on two patches I sent previously, [1/6] that makes
cpufreq_update_util() use RCU-sched (one change from the previous version
as requested by Peter) and [2/6] that reworks acpi-cpufreq so the fast
switching (added later in patch [5/6]) can work with all of the frequency
setting methods the driver may use.

Comments welcome.

Thanks,
Rafael

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[PATCH 0/6] cpufreq: schedutil governor "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-02 03:30 +0100
  [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler utilization data "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-02 03:30 +0100
    Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-02 18:20 +0100
      Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-02 19:00 +0100
        Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-02 23:50 +0100
          Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 13:30 +0100
            Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Juri Lelli <juri.lelli@arm.com> - 2016-03-03 13:40 +0100
            Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-03 17:30 +0100
              Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 17:40 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 17:50 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-04 02:20 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 18:00 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Juri Lelli <juri.lelli@arm.com> - 2016-03-03 18:20 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Juri Lelli <juri.lelli@arm.com> - 2016-03-03 18:00 +0100
          Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-03 15:10 +0100
            Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 16:40 +0100
              Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 17:30 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 17:50 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-03 18:30 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Peter Zijlstra <peterz@infradead.org> - 2016-03-03 19:30 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Dietmar Eggemann <dietmar.eggemann@arm.com> - 2016-03-03 20:20 +0100
                Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-03 20:00 +0100
        Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Vincent Guittot <vincent.guittot@linaro.org> - 2016-03-03 14:10 +0100
          Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Steve Muckle <steve.muckle@linaro.org> - 2016-03-03 21:10 +0100
            Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data "Rafael J. Wysocki" <rafael@kernel.org> - 2016-03-03 21:30 +0100
              Re: [PATCH 6/6] cpufreq: schedutil: New governor based on scheduler  utilization data Steve Muckle <steve.muckle@linaro.org> - 2016-03-03 22:40 +0100
  [PATCH v2 10/10] cpufreq: schedutil: New governor based on scheduler utilization data "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
  [PATCH v2 6/10] cpufreq: Support for fast frequency switching "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
  [PATCH v2 0/10] cpufreq: schedutil governor "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
    [PATCH v2 1/10] cpufreq: Reduce cpufreq_update_util() overhead a bit "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
    [PATCH v2 5/10] cpufreq: Move governor attribute set headers to cpufreq.h "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
      Re: [PATCH v2 5/10] cpufreq: Move governor attribute set headers to  cpufreq.h Viresh Kumar <viresh.kumar@linaro.org> - 2016-03-04 07:00 +0100
    [PATCH v2 2/10][Resend] cpufreq: acpi-cpufreq: Make read and write operations more efficient "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
    [PATCH v2 3/10] cpufreq: governor: New data type for management part of dbs_data "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
      Re: [PATCH v2 3/10] cpufreq: governor: New data type for management  part of dbs_data Viresh Kumar <viresh.kumar@linaro.org> - 2016-03-04 07:00 +0100
    [PATCH v2 7/10] cpufreq: Rework the scheduler hooks for triggering updates "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
    [PATCH v2 4/10] cpufreq: governor: Move abstract gov_attr_set code to seperate file "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
      Re: [PATCH v2 4/10] cpufreq: governor: Move abstract gov_attr_set  code to seperate file Viresh Kumar <viresh.kumar@linaro.org> - 2016-03-04 07:00 +0100
    [PATCH v2 8/10] cpufreq: Move scheduler-related code to the sched directory "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100
    [PATCH v2 9/10] cpufreq: sched: Re-introduce cpufreq_update_util() "Rafael J. Wysocki" <rjw@rjwysocki.net> - 2016-03-04 04:40 +0100

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