Subject: Re: Random high CPU utilization in blk-mq with the none scheduler
To:     Dexuan Cui <decui@microsoft.com>,
        "'ming.lei@redhat.com'" <ming.lei@redhat.com>,
        'Christoph Hellwig' <hch@lst.de>,
        "'linux-block@vger.kernel.org'" <linux-block@vger.kernel.org>
Cc:     Long Li <longli@microsoft.com>,
        "Michael Kelley (LINUX)" <mikelley@microsoft.com>,
        "'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <bb696622-38ee-c582-ce70-5bfa632f8989@kernel.dk>
Date:   Mon, 13 Dec 2021 11:43:02 -0700
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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