Re: [PATCH v4] sched,fair: Skip newidle_balance if a wakeup is pending

[Mel Gorman]

On Thu, Apr 22, 2021 at 01:02:36PM -0400, Rik van Riel wrote:
> 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@xxxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs