[RFC PATCH 0/3] CFS idle injection

Jacob Pan
2015-11-03T00:12:16Z

Hi Peter and all,

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 | 345 +++++++++++++++++++++++++++++++++++++++++++
kernel/sched/sched.h | 3 +
kernel/sysctl.c | 20 +++
kernel/time/tick-sched.c | 2 +-
9 files changed, 427 insertions(+), 1 deletion(-)

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1.9.1