From: Sasha Levin <sashal@xxxxxxxxxx> Sent: Monday, December 20, 2021 5:58 PM > > From: Jens Axboe <axboe@xxxxxxxxx> > > [ Upstream commit cb2ac2912a9ca7d3d26291c511939a41361d2d83 ] > > 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@xxxxxxxxxxxxx> > Link: https://lore.kernel.org/linux-block/BYAPR21MB1270C598ED214C0490F47400BF719@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > Reviewed-by: Ming Lei <ming.lei@xxxxxxxxxx> > Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> > --- > block/blk-core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/block/blk-core.c b/block/blk-core.c > index c2d912d0c976c..a728434fcff87 100644 > --- a/block/blk-core.c > +++ b/block/blk-core.c > @@ -1625,6 +1625,8 @@ 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); > -- > 2.34.1 Sasha -- there are reports of this patch causing performance problems. See https://lore.kernel.org/lkml/1639853092.524jxfaem2.none@localhost/. I would suggest *not* backporting it to any of the stable branches until the issues are fully sorted out. Michael
