sched/core: Accounting forceidle time for all tasks except idle task

There are two types of forced idle time: forced idle time from cookie'd
task and forced idle time form uncookie'd task. The forced idle time from
uncookie'd task is actually caused by the cookie'd task in runqueue
indirectly, and it's more accurate to measure the capacity loss with the
sum of both.

Assuming cpu x and cpu y are a pair of SMT siblings, consider the
following scenarios:
  1.There's a cookie'd task running on cpu x, and there're 4 uncookie'd
    tasks running on cpu y. For cpu x, there will be 80% forced idle time
    (from uncookie'd task); for cpu y, there will be 20% forced idle time
    (from cookie'd task).
  2.There's a uncookie'd task running on cpu x, and there're 4 cookie'd
    tasks running on cpu y. For cpu x, there will be 80% forced idle time
    (from cookie'd task); for cpu y, there will be 20% forced idle time
    (from uncookie'd task).

The scenario1 can recurrent by stress-ng(scenario2 can recurrent similary):
    (cookie'd)taskset -c x stress-ng -c 1 -l 100
    (uncookie'd)taskset -c y stress-ng -c 4 -l 100

In the above two scenarios, the total capacity loss is 1 cpu, but in
scenario1, the cookie'd forced idle time tells us 20% cpu capacity loss, in
scenario2, the cookie'd forced idle time tells us 80% cpu capacity loss,
which are not accurate. It'll be more accurate to measure with cookie'd
forced idle time and uncookie'd forced idle time.

Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Josh Don <joshdon@google.com>
Link: https://lore.kernel.org/r/1641894961-9241-2-git-send-email-CruzZhao@linux.alibaba.com

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 83872f95a1ea2af92378c6055f3221feed797eb3..0d2ab2a2f9feb8213b5613144a63463fd79fcb07 100644 (file)
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5822,8 +5822,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
        }
 
        if (schedstat_enabled() && rq->core->core_forceidle_count) {
-               if (cookie)
-                       rq->core->core_forceidle_start = rq_clock(rq->core);
+               rq->core->core_forceidle_start = rq_clock(rq->core);
                rq->core->core_forceidle_occupation = occ;
        }
 

diff --git a/kernel/sched/core_sched.c b/kernel/sched/core_sched.c
index 1fb45672ec85060d42f56d742526930e0e3c2202..c8746a9a7ada336291137da17376fce6d5529f3c 100644 (file)
--- a/kernel/sched/core_sched.c
+++ b/kernel/sched/core_sched.c
@@ -277,7 +277,7 @@ void __sched_core_account_forceidle(struct rq *rq)
                rq_i = cpu_rq(i);
                p = rq_i->core_pick ?: rq_i->curr;
 
-               if (!p->core_cookie)
+               if (p == rq_i->idle)
                        continue;
 
                __schedstat_add(p->stats.core_forceidle_sum, delta);