Re: Random high CPU utilization in blk-mq with the none scheduler

Jens Axboe
2021-12-13T18:43:08Z

On 12/11/21 11:54 AM, Dexuan Cui wrote:
>> From: Jens Axboe <axboe@kernel.dk>
>> Sent: Saturday, December 11, 2021 6:21 AM
>>
>> Sorry, can you do:
>>
>> # perf report -g --no-children
>>
>> instead?
>
> Attached.

I wonder if this will help, SCSI artifact making us hit the
mod delayed work path all the time. Might be a race in there,
but should be fine for testing.

diff --git a/block/blk-core.c b/block/blk-core.c
index 4d8f5fe91588..cb2f4d604bad 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1625,7 +1625,9 @@ EXPORT_SYMBOL(kblockd_schedule_work);
int kblockd_mod_delayed_work_on(int cpu, struct delayed_work *dwork,
unsigned long delay)
{
- return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
+ if (!work_pending(&dwork->work))
+ return mod_delayed_work_on(cpu, kblockd_workqueue, dwork, delay);
+ return true;
}
EXPORT_SYMBOL(kblockd_mod_delayed_work_on);

--
Jens Axboe