This patch series implements an alternative window assisted load tracking mechanism in lieu of PELT based cpu utilization tracking. Testing has shown that a window based non-decaying metric such as WALT guiding cpu frequency and task placement decisions can improve performance/power especially when running workloads more commonly found on mobile devices. The aim of this series is to incorporate WALT accounting into the scheduler and feed WALT statistics to schedutil in order to guide cpu frequency selection. The implementation is detailed in the commit text of Patch 1. The eventual goal is to also guide placement decisions based on WALT statistics.

WALT has existed in out-of-tree kernels for ARM/ARM64 commercialized devices for a few years. This is an effort to bring WALT to mainline as well as to test on multiple architectures and with varied workloads.

This RFC version is mainly to preview what the code will look like on mainline. Future RFC revisions will include a theoretical discussion and benchmark results.

Tested on an Intel x86_64 machine (on top of 4.7-rc6). (Benchmark results will be sent out separately and as part of this message in the next RFC version).

Patch 1: Adds WALT tracking to the scheduler

Patches 2-3: Temporary patches to bring in EAS/sched-freq like capacity table and to use Intel PMC counters for more accurate frequency invariant load tracking on X86. Included for completeness but not meant for merging.

include/linux/sched.h | 35 ++++++++++ include/linux/sched/sysctl.h | 2 + include/trace/events/sched.h | 76 +++++++++++++++++++++ init/Kconfig | 9 +++ kernel/sched/Makefile | 1 + kernel/sched/core.c | 29 ++++++++- kernel/sched/cpufreq_schedutil.c | 44 ++++++++++++- kernel/sched/cputime.c | 11 +++- kernel/sched/debug.c | 10 +++ kernel/sched/fair.c | 7 +- kernel/sched/sched.h | 13 ++++ kernel/sched/walt.c | 580 ++++++++++++++++++++++++++++++++++ kernel/sched/walt.h | 75 +++++++++++++++++++++ kernel/sysctl.c | 18 +++++ 14 files changed, 904 insertions(+), 6 deletions(-)

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