maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I5F6X6
CVE: NA

Reference: https://lore.kernel.org/all/20210916162451.709260-1-guro@fb.com/

-------------------

This patch adds 3 hooks to control wakeup and tick preemption:
  cfs_check_preempt_tick
  cfs_check_preempt_wakeup
  cfs_wakeup_preempt_entity

The first one allows to force or suppress a preemption from a tick
context. An obvious usage example is to minimize the number of
non-voluntary context switches and decrease an associated latency
penalty by (conditionally) providing tasks or task groups an extended
execution slice. It can be used instead of tweaking
sysctl_sched_min_granularity.

The second one is called from the wakeup preemption code and allows
to redefine whether a newly woken task should preempt the execution
of the current task. This is useful to minimize a number of
preemptions of latency sensitive tasks. To some extent it's a more
flexible analog of a sysctl_sched_wakeup_granularity.

The third one is similar, but it tweaks the wakeup_preempt_entity()
function, which is called not only from a wakeup context, but also
from pick_next_task(), which allows to influence the decision on which
task will be running next.

It's a place for a discussion whether we need both these hooks or only
one of them: the second is more powerful, but depends more on the
current implementation. In any case, bpf hooks are not an ABI, so it's
not a deal breaker.

The idea of the wakeup_preempt_entity hook belongs to Rik van Riel. He
also contributed a lot to the whole patchset by proving his ideas,
recommendations and a feedback for earlier (non-public) versions.
Signed-off-by: NRoman Gushchin <guro@fb.com>
Signed-off-by: NChen Hui <judy.chenhui@huawei.com>
Signed-off-by: NRen Zhijie <renzhijie2@huawei.com>