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authorBarry Song <song.bao.hua@hisilicon.com>2021-10-16 19:11:09 +0800
committerPeter Zijlstra <peterz@infradead.org>2021-12-07 15:14:10 +0100
commit2917406c352757642c3c1a13a4c99c96e6d22fde (patch)
tree5b3dc47b074fd18d268660b51b299eff8e92498a /kernel/sched/fair.c
parent014ba44e8184e1acf93e0cbb7089ee847802f8f0 (diff)
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/sched/fair.c')
-rw-r--r--kernel/sched/fair.c5
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)