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From: John Garry <john.garry@huawei.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Bart Van Assche <bvanassche@acm.org>,
	"Hannes Reinecke" <hare@suse.com>, Christoph Hellwig <hch@lst.de>,
	Thomas Gleixner <tglx@linutronix.de>,
	Keith Busch <keith.busch@intel.com>
Subject: Re: [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug
Date: Tue, 29 Oct 2019 17:54:50 +0000	[thread overview]
Message-ID: <6c0f94be-3ec7-974f-3a67-7d715a374c6a@huawei.com> (raw)
In-Reply-To: <20191029100509.GC20854@ming.t460p>

On 29/10/2019 10:05, Ming Lei wrote:
>>> But this patch does wait for completion of in-flight request before
>>> shutdown the last CPU of this hctx.
>>>
>> Hi Ming,
>>
>> It may actually be a request from a hctx which is not shut down which errors
>> and causes the time out. I'm still checking.
> If that is the case, blk_mq_hctx_drain_inflight_rqs() will wait for
> completion of this request.
> 
> The only chance it is missed is that the last CPU of this hctx becomes
> offline just when this request stays in request list after it is
> retried from EH.
> 
>> BTW, Can you let me know exactly where you want the debug for "Or
>> blk_mq_hctx_next_cpu() may still run WORK_CPU_UNBOUND schedule after
>> all CPUs are offline, could you add debug message in that branch?"
> You can add the following debug message, then reproduce the issue and
> see if the debug log is dumped.
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 06081966549f..5a98a7b79c0d 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1452,6 +1452,10 @@ static int blk_mq_hctx_next_cpu(struct blk_mq_hw_ctx *hctx)
>   		 */
>   		hctx->next_cpu = next_cpu;
>   		hctx->next_cpu_batch = 1;
> +
> +		printk(KERN_WARNING "CPU %d, schedule from (dead) hctx %s\n",
> +			raw_smp_processor_id(),
> +			cpumask_empty(hctx->cpumask) ? "inactive": "active");
>   		return WORK_CPU_UNBOUND;

We don't seem to be hitting this.

So the error generally happens after the CPUs have been hot unplugged 
for some time. I find a SCSI IO errors in the LLDD, having been run on 
an up hctx - blk-mq requeues it on same hctx, but it only dispatches 
eventually after some other SCSI IO timesout - I assume that IO timesout 
due to earlier scsi_set_blocked() call.

Continuing to look....

Thanks,
John

>   	}
>   
> 
> Thanks,
> Ming
> 
> .


  reply	other threads:[~2019-10-29 17:54 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-14  1:50 Ming Lei
2019-10-14  1:50 ` [PATCH V4 1/5] blk-mq: add new state of BLK_MQ_S_INTERNAL_STOPPED Ming Lei
2019-10-14  1:50 ` [PATCH V4 2/5] blk-mq: prepare for draining IO when hctx's all CPUs are offline Ming Lei
2019-10-14  1:50 ` [PATCH V4 3/5] blk-mq: stop to handle IO and drain IO before hctx becomes dead Ming Lei
2019-11-28  9:29   ` John Garry
2019-10-14  1:50 ` [PATCH V4 4/5] blk-mq: re-submit IO in case that hctx is dead Ming Lei
2019-10-14  1:50 ` [PATCH V4 5/5] blk-mq: handle requests dispatched from IO scheduler " Ming Lei
2019-10-16  8:58 ` [PATCH V4 0/5] blk-mq: improvement on handling IO during CPU hotplug John Garry
2019-10-16 12:07   ` Ming Lei
2019-10-16 16:19     ` John Garry
     [not found]       ` <55a84ea3-647d-0a76-596c-c6c6b2fc1b75@huawei.com>
2019-10-20 10:14         ` Ming Lei
2019-10-21  9:19           ` John Garry
2019-10-21  9:34             ` Ming Lei
2019-10-21  9:47               ` John Garry
2019-10-21 10:24                 ` Ming Lei
2019-10-21 11:49                   ` John Garry
2019-10-21 12:53                     ` Ming Lei
2019-10-21 14:02                       ` John Garry
2019-10-22  0:16                         ` Ming Lei
2019-10-22 11:19                           ` John Garry
2019-10-22 13:45                             ` Ming Lei
2019-10-25 16:33             ` John Garry
2019-10-28 10:42               ` Ming Lei
2019-10-28 11:55                 ` John Garry
2019-10-29  1:50                   ` Ming Lei
2019-10-29  9:22                     ` John Garry
2019-10-29 10:05                       ` Ming Lei
2019-10-29 17:54                         ` John Garry [this message]
2019-10-31 16:28                         ` John Garry
2019-11-28  1:09 ` chenxiang (M)
2019-11-28  2:02   ` Ming Lei
2019-11-28 10:45     ` John Garry

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