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| author | Rik van Riel <riel@surriel.com> | 2021-04-22 19:02:36 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2021-05-12 11:43:23 +0200 |
| commit | e5e678e4fea26d73444f4427cbbaeab4fa79ecee (patch) | |
| tree | 87538ce381a47c6ec2b6edbfc90e7b67159002cd /kernel/sched/fair.c | |
| parent | sched/core: Remove the pointless BUG_ON(!task) from wake_up_q() (diff) | |
| download | linux-e5e678e4fea26d73444f4427cbbaeab4fa79ecee.tar.xz linux-e5e678e4fea26d73444f4427cbbaeab4fa79ecee.zip | |
sched,fair: Skip newidle_balance if a wakeup is pending
The try_to_wake_up function has an optimization where it can queue
a task for wakeup on its previous CPU, if the task is still in the
middle of going to sleep inside schedule().
Once schedule() re-enables IRQs, the task will be woken up with an
IPI, and placed back on the runqueue.
If we have such a wakeup pending, there is no need to search other
CPUs for runnable tasks. Just skip (or bail out early from) newidle
balancing, and run the just woken up task.
For a memcache like workload test, this reduces total CPU use by
about 2%, proportionally split between user and system time,
and p99 and p95 application response time by 10% on average.
The schedstats run_delay number shows a similar improvement.
Signed-off-by: Rik van Riel <riel@surriel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
Acked-by: Mel Gorman <mgorman@suse.de>
Link: https://lkml.kernel.org/r/20210422130236.0bb353df@imladris.surriel.com
Diffstat (limited to '')
| -rw-r--r-- | kernel/sched/fair.c | 11 |
1 files changed, 10 insertions, 1 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3248e24a90b0..d10c6cc4609c 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -10592,6 +10592,14 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) u64 curr_cost = 0; update_misfit_status(NULL, this_rq); + + /* + * There is a task waiting to run. No need to search for one. + * Return 0; the task will be enqueued when switching to idle. + */ + if (this_rq->ttwu_pending) + return 0; + /* * We must set idle_stamp _before_ calling idle_balance(), such that we * measure the duration of idle_balance() as idle time. @@ -10657,7 +10665,8 @@ static int newidle_balance(struct rq *this_rq, struct rq_flags *rf) * Stop searching for tasks to pull if there are * now runnable tasks on this rq. */ - if (pulled_task || this_rq->nr_running > 0) + if (pulled_task || this_rq->nr_running > 0 || + this_rq->ttwu_pending) break; } rcu_read_unlock(); |