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[RFC PATCH v2 0/3] CFS idle injection

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  [RFC PATCH v2 0/3] CFS idle injection Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 01:30 +0100
    [RFC PATCH v2 1/3] ktime: add a roundup function Jacob Pan <jacob.jun.pan@linux.intel.com> - 2015-11-10 01:30 +0100

#1266120 — [RFC PATCH v2 0/3] CFS idle injection

Hi Peter and all,

Changes since initial RFC:
	- integrated Peter's patch to optimize hot path
	- check softirq, allow softirqd
	- changed tracing function to include string message

Kconfig is not changed, wanted to hear more feedback. Whether this should be
a CONFIG option since we already optimized for the hot path.


Intro:
A while ago, we had discussion about how powerclamp is broken in the
sense of turning off idle ticks in the forced idle period.
https://lkml.org/lkml/2014/12/18/369

It was suggested to replace the current kthread play idle loop with a
timer based runqueue throttling scheme. I finally got around to implement
this and code is much simpler. I also have good test results in terms of
efficiency, scalability, etc.
http://events.linuxfoundation.org/sites/events/files/slides/LinuxCon_Japan_2015_idle_injection1_0.pdf
slide #18+ shows the data on client and server.

I have two choices for this code:
1) be part of existing powerclamp driver but require exporting some
   sched APIs.
2) be part of sched since the genernal rule applies when it comes down
   to sycnhronized idle time for best power savings.

The patches below are for #2. There is a known problem with LOW RES timer
mode that I am working on. But I am hoping to get review earlier.

We are entering a very power limited environment on client side, frequency
scaling can only be efficient at certain range. e.g. on SKL, upto ~900MHz,
anything below, it is increasingly more efficient to do C-states insertion
if coordinated.

Looking forward, there are use case beyond thermal/power capping. I think
we can consolidate ballanced partial busy workload that are evenly
distributed among CPUs.

Please let me know what you think.

Thanks,



Jacob Pan (3):
  ktime: add a roundup function
  timer: relax tick stop in idle entry
  sched: introduce synchronized idle injection

 include/linux/ktime.h        |  10 ++
 include/linux/sched.h        |  12 ++
 include/linux/sched/sysctl.h |   5 +
 include/trace/events/sched.h |  23 +++
 init/Kconfig                 |   8 +
 kernel/sched/fair.c          | 381 ++++++++++++++++++++++++++++++++++++++++++-
 kernel/sched/sched.h         |   2 +-
 kernel/sysctl.c              |  20 +++
 kernel/time/tick-sched.c     |   2 +-
 9 files changed, 457 insertions(+), 6 deletions(-)

-- 
1.9.1

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#1266123 — [RFC PATCH v2 1/3] ktime: add a roundup function

ktime roundup function can be used to keep timer aligned and
prevent drift for recurring timeouts.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
---
 include/linux/ktime.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index 2b6a204..2e293fa 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -233,6 +233,16 @@ static inline ktime_t ktime_sub_us(const ktime_t kt, const u64 usec)
 
 extern ktime_t ktime_add_safe(const ktime_t lhs, const ktime_t rhs);
 
+static inline ktime_t ktime_roundup(ktime_t x, ktime_t y)
+{
+	u64 temp_tv64;
+
+	temp_tv64 = x.tv64 + y.tv64 - 1;
+	temp_tv64 = div64_u64(temp_tv64, y.tv64);
+	x.tv64 = temp_tv64 * y.tv64;
+
+	return x;
+}
 /**
  * ktime_to_timespec_cond - convert a ktime_t variable to timespec
  *			    format only if the variable contains data
-- 
1.9.1

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