block: reduce kblockd_mod_delayed_work_on() CPU consumption

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/
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/blk-core.c b/block/blk-core.c
index 1378d084c770f6641a911caf8d98d302026fa689..c1833f95cb9728eb3023255fc4e0c42711ded297 100644 (file)
--- 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);
 }
 EXPORT_SYMBOL(kblockd_mod_delayed_work_on);