[RFC PATCH 0/2] Makes it easier for the wakee to choose previous CPU

[Chen Yu]

When task p is woken up, the scheduler leverages select_idle_sibling()
to find an idle CPU for it. p's previous CPU is usually a preference
because it can improve cache locality. However in many cases the
previous CPU has already been taken by other wakees, thus p has to
find another idle CPU.

Inhit the task migration while keeping the work conservation of
scheduler could benefit many workloads. Inspired by Mathieu's
proposal to limit the task migration ratio[1], this patch takes
the task average sleep duration into consideration. If the
task is a short sleeping one, then tag its previous CPU as cache
hot for a short while. During this tag period, other wakees are
not allowed to pick this idle CPU until a timeout. Later if the
task is woken up again, it can find its previous CPU still be
idle, and chooses it in select_idle_sibling().

The benchmark from netperf has shown some improvement, which is
described in patch 2/2.

This series is based on the tip/sched/core on top of
Commit 3f4feb58037a ("sched: Misc cleanups").

It would be appreciated for any feedback/comments.

Link: https://lore.kernel.org/lkml/20230905171105.1005672-2-mathieu.desnoyers@xxxxxxxxxxxx/ #1

Chen Yu (2):
  sched/fair: Record the average sleep time of a task
  sched/fair: skip the cache hot CPU in select_idle_cpu()

 include/linux/sched.h   |  3 +++
 kernel/sched/fair.c     | 47 ++++++++++++++++++++++++++++++++++++++---
 kernel/sched/features.h |  1 +
 kernel/sched/sched.h    |  1 +
 4 files changed, 49 insertions(+), 3 deletions(-)

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2.25.1