[PATCH RESEND v4 0/2] sched: Queue task on wakelist in the same llc if the wakee cpu is idle

[Tianchen Ding <dtcccc@linux.alibaba.com>]

Wakelist can help avoid cache bouncing and offload the overhead of waker
cpu. So far, using wakelist within the same llc only happens on
WF_ON_CPU, and this limitation could be removed to further improve
wakeup performance. The result of Unixbench Pipe-based Context Switching
can be improved up to ~10%.

The 1st patch introduces a more "correct" way to check whether the wakee
cpu is soon-to-be-idle.

The 2nd patch allows using wakelist in any case when the wakee cpu is
idle or soon-to-be-idle.

v4:
Add benchmark results about the 1st patch.
Modify some comments.

v3: https://lore.kernel.org/all/20220602040645.275555-1-dtcccc@linux.alibaba.com/
Add a patch to fix the check of nr_running.
After that, we can remove WF_ON_CPU to achieve the same purpose.
Thank Valentin and Mel.

v2: https://lore.kernel.org/all/20220527090544.527411-1-dtcccc@linux.alibaba.com/
Modify commit log to describe key point in detail.
Add more benchmark results on more archs.

v1: https://lore.kernel.org/all/20220513062427.2375743-1-dtcccc@linux.alibaba.com/

Tianchen Ding (2):
  sched: Fix the check of nr_running at queue wakelist
  sched: Remove the limitation of WF_ON_CPU on wakelist if wakee cpu is
    idle

 kernel/sched/core.c  | 30 ++++++++++++++++++------------
 kernel/sched/sched.h |  1 -
 2 files changed, 18 insertions(+), 13 deletions(-)

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2.27.0