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| author |   Barry Song <song.bao.hua@hisilicon.com> | 2021-10-16 19:11:09 +0800 |
|---|---|---|
| committer |   Peter Zijlstra <peterz@infradead.org> | 2021-12-07 15:14:10 +0100 |
| commit | 2917406c352757642c3c1a13a4c99c96e6d22fde (patch) | |
| tree | 5b3dc47b074fd18d268660b51b299eff8e92498a /kernel | |
| parent | sched/fair: Fix per-CPU kthread and wakee stacking for asym CPU capacity (diff) | |
| download | linux-dev-2917406c352757642c3c1a13a4c99c96e6d22fde.tar.xz linux-dev-2917406c352757642c3c1a13a4c99c96e6d22fde.zip | |
sched/fair: Document the slow path and fast path in select_task_rq_fair
All People I know including myself took a long time to figure out that
typical wakeup will always go to fast path and never go to slow path
except WF_FORK and WF_EXEC.
Vincent reminded me once in a linaro meeting and made me understand
slow path won't happen for WF_TTWU. But my other friends repeatedly
wasted a lot of time on testing this path like me before I reminded
them.
So obviously the code needs some document.
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211016111109.5559-1-21cnbao@gmail.com
Diffstat (limited to 'kernel')
| -rw-r--r-- | kernel/sched/fair.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 06722188df49..f34f2f344fe9 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6917,6 +6917,11 @@ select_task_rq_fair(struct task_struct *p, int prev_cpu, int wake_flags) break; } + /* + * Usually only true for WF_EXEC and WF_FORK, as sched_domains + * usually do not have SD_BALANCE_WAKE set. That means wakeup + * will usually go to the fast path. + */ if (tmp->flags & sd_flag) sd = tmp; else if (!want_affine) |