Re: [PATCH v2] block: reduce kblockd_mod_delayed_work_on() CPU consumption

[Ming Lei <ming.lei@redhat.com>]

On Tue, Dec 14, 2021 at 01:49:34PM -0700, Jens Axboe wrote:
> Dexuan reports that he's seeing spikes of very heavy CPU utilization when
> running 24 disks and using the 'none' scheduler. This happens off the
> sched restart path, because SCSI requires the queue to be restarted async,
> and hence we're hammering on mod_delayed_work_on() to ensure that the work
> item gets run appropriately.
> 
> Avoid hammering on the timer and just use queue_work_on() if no delay
> has been specified.
> 
> Reported-and-tested-by: Dexuan Cui <decui@microsoft.com>
> Link: https://lore.kernel.org/linux-block/BYAPR21MB1270C598ED214C0490F47400BF719@BYAPR21MB1270.namprd21.prod.outlook.com/
> Signed-off-by: Jens Axboe <axboe@kernel.dk>
> 
> ---
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 1378d084c770..c1833f95cb97 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -1484,6 +1484,8 @@ EXPORT_SYMBOL(kblockd_schedule_work);
>  int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
>  				unsigned long delay)
>  {
> +	if (!delay)
> +		return queue_work_on(cpu, kblockd_workqueue, &dwork->work);
>  	return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);

Reviewed-by: Ming Lei <ming.lei@redhat.com>


Thanks,
Ming