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From: Ming Lei <ming.lei@redhat.com>
To: Bart Van Assche <Bart.VanAssche@wdc.com>
Cc: "axboe@kernel.dk" <axboe@kernel.dk>,
	"dm-devel@redhat.com" <dm-devel@redhat.com>,
	"hch@infradead.org" <hch@infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	"osandov@fb.com" <osandov@fb.com>,
	"snitzer@redhat.com" <snitzer@redhat.com>
Subject: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle
Date: Fri, 19 Jan 2018 15:34:23 +0800	[thread overview]
Message-ID: <20180119073423.GC25369@ming.t460p> (raw)
In-Reply-To: <1516338585.4077.1.camel@wdc.com>

On Fri, Jan 19, 2018 at 05:09:46AM +0000, Bart Van Assche wrote:
> On Fri, 2018-01-19 at 10:32 +0800, Ming Lei wrote:
> > Now most of times both NVMe and SCSI won't return BLK_STS_RESOURCE, and
> > it should be DM-only which returns STS_RESOURCE so often.
> 
> That's wrong at least for SCSI. See also https://marc.info/?l=linux-block&m=151578329417076.
> 

> For other scenario's, e.g. if a SCSI initiator submits a
> SCSI request over a fabric and the SCSI target replies with "BUSY" then the

Could you explain a bit when SCSI target replies with BUSY very often?

Inside initiator, we have limited the max per-LUN requests and per-host
requests already before calling .queue_rq().

> SCSI core will end the I/O request with status BLK_STS_RESOURCE after the
> maximum number of retries has been reached (see also scsi_io_completion()).
> In that last case, if a SCSI target sends a "BUSY" reply over the wire back
> to the initiator, there is no other approach for the SCSI initiator to
> figure out whether it can queue another request than to resubmit the
> request. The worst possible strategy is to resubmit a request immediately
> because that will cause a significant fraction of the fabric bandwidth to
> be used just for replying "BUSY" to requests that can't be processed
> immediately.


-- 
Ming

  reply	other threads:[~2018-01-19  7:34 UTC|newest]

Thread overview: 80+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-18  2:41 [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle Ming Lei
2018-01-18 16:50 ` Bart Van Assche
2018-01-18 17:03   ` Mike Snitzer
2018-01-18 17:03     ` Mike Snitzer
2018-01-18 17:20     ` Bart Van Assche
2018-01-18 17:20       ` Bart Van Assche
2018-01-18 18:30       ` Mike Snitzer
2018-01-18 18:47         ` Bart Van Assche
2018-01-18 18:47           ` Bart Van Assche
2018-01-18 20:11           ` Jens Axboe
2018-01-18 20:11             ` Jens Axboe
2018-01-18 20:48             ` Mike Snitzer
2018-01-18 20:58               ` Bart Van Assche
2018-01-18 20:58                 ` Bart Van Assche
2018-01-18 21:23                 ` Mike Snitzer
2018-01-18 21:23                   ` Mike Snitzer
2018-01-18 21:37                   ` Laurence Oberman
2018-01-18 21:39                   ` [dm-devel] " Bart Van Assche
2018-01-18 21:39                     ` Bart Van Assche
2018-01-18 21:45                     ` Laurence Oberman
2018-01-18 21:45                       ` Laurence Oberman
2018-01-18 22:01                     ` Mike Snitzer
2018-01-18 22:18                       ` Laurence Oberman
2018-01-18 22:20                         ` Laurence Oberman
2018-01-18 22:20                           ` Laurence Oberman
2018-01-18 22:24                         ` Bart Van Assche
2018-01-18 22:24                           ` Bart Van Assche
2018-01-18 22:35                           ` Laurence Oberman
2018-01-18 22:39                             ` Jens Axboe
2018-01-18 22:55                               ` Bart Van Assche
2018-01-18 22:55                                 ` Bart Van Assche
2018-01-18 22:20                       ` Bart Van Assche
2018-01-18 22:20                         ` Bart Van Assche
2018-01-23  9:22                         ` [PATCH] block: neutralize blk_insert_cloned_request IO stall regression (was: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle) Mike Snitzer
2018-01-23 10:53                           ` Ming Lei
2018-01-23 12:15                             ` Mike Snitzer
2018-01-23 12:17                               ` Ming Lei
2018-01-23 12:43                                 ` Mike Snitzer
2018-01-23 16:43                           ` [PATCH] " Bart Van Assche
2018-01-23 16:43                             ` Bart Van Assche
2018-01-19  2:32             ` [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle Ming Lei
2018-01-19  4:02               ` Jens Axboe
2018-01-19  7:26                 ` Ming Lei
2018-01-19 15:20                   ` Bart Van Assche
2018-01-19 15:20                     ` Bart Van Assche
2018-01-19 15:25                     ` Jens Axboe
2018-01-19 15:33                     ` Ming Lei
2018-01-19 16:06                       ` Bart Van Assche
2018-01-19 16:06                         ` Bart Van Assche
2018-01-19 15:24                   ` Jens Axboe
2018-01-19 15:40                     ` Ming Lei
2018-01-19 15:40                       ` Ming Lei
2018-01-19 15:48                       ` Jens Axboe
2018-01-19 16:05                         ` Ming Lei
2018-01-19 16:19                           ` Jens Axboe
2018-01-19 16:26                             ` Ming Lei
2018-01-19 16:27                               ` Jens Axboe
2018-01-19 16:37                                 ` Ming Lei
2018-01-19 16:41                                   ` Jens Axboe
2018-01-19 16:41                                     ` Jens Axboe
2018-01-19 16:47                                     ` Mike Snitzer
2018-01-19 16:52                                       ` Jens Axboe
2018-01-19 17:05                                         ` Ming Lei
2018-01-19 17:09                                           ` Jens Axboe
2018-01-19 17:20                                             ` Ming Lei
2018-01-19 17:38                                   ` Jens Axboe
2018-01-19 18:24                                     ` Ming Lei
2018-01-19 18:24                                       ` Ming Lei
2018-01-19 18:33                                     ` Mike Snitzer
2018-01-19 23:52                                     ` Ming Lei
2018-01-20  4:27                                       ` Jens Axboe
2018-01-19 16:13                         ` Mike Snitzer
2018-01-19 16:23                           ` Jens Axboe
2018-01-19 23:57                             ` Ming Lei
2018-01-29 22:37                     ` Bart Van Assche
2018-01-19  5:09               ` Bart Van Assche
2018-01-19  5:09                 ` Bart Van Assche
2018-01-19  7:34                 ` Ming Lei [this message]
2018-01-19 19:47                   ` Bart Van Assche
2018-01-19 19:47                     ` Bart Van Assche

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