From: Bart Van Assche <bart.vanassche@wdc.com>
To: Jens Axboe <axboe@kernel.dk>, Ming Lei <ming.lei@redhat.com>
Cc: "snitzer@redhat.com" <snitzer@redhat.com>,
"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>
Subject: Re: [RFC PATCH] blk-mq: fixup RESTART when queue becomes idle
Date: Mon, 29 Jan 2018 14:37:00 -0800 [thread overview]
Message-ID: <bb221027-3fcf-fbf8-7535-05569fb850ca@wdc.com> (raw)
In-Reply-To: <047f68ec-f51b-190f-2f89-f413325c2540@kernel.dk>
On 01/19/18 07:24, Jens Axboe wrote:
> That's what I thought. So for a low queue depth underlying queue, it's
> quite possible that this situation can happen. Two potential solutions
> I see:
>
> 1) As described earlier in this thread, having a mechanism for being
> notified when the scarce resource becomes available. It would not
> be hard to tap into the existing sbitmap wait queue for that.
>
> 2) Have dm set BLK_MQ_F_BLOCKING and just sleep on the resource
> allocation. I haven't read the dm code to know if this is a
> possibility or not.
>
> I'd probably prefer #1. It's a classic case of trying to get the
> request, and if it fails, add ourselves to the sbitmap tag wait
> queue head, retry, and bail if that also fails. Connecting the
> scarce resource and the consumer is the only way to really fix
> this, without bogus arbitrary delays.
(replying to an e-mail from ten days ago)
Implementing a notification mechanism for all cases in which
blk_insert_cloned_request() returns BLK_STS_RESOURCE today would require
a lot of work. If e.g. a SCSI LLD returns one of the SCSI_MLQUEUE_*_BUSY
return codes from its .queuecommand() implementation then the SCSI core
will translate that return code into BLK_STS_RESOURCE. From scsi_queue_rq():
reason = scsi_dispatch_cmd(cmd);
if (reason) {
scsi_set_blocked(cmd, reason);
ret = BLK_STS_RESOURCE;
goto out_dec_host_busy;
}
In other words, implementing a notification mechanism for all cases in
which blk_insert_cloned_request() can return BLK_STS_RESOURCE would
require to modify all SCSI LLDs.
Bart.
next prev parent reply other threads:[~2018-01-29 22:37 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 [this message]
2018-01-19 5:09 ` Bart Van Assche
2018-01-19 5:09 ` Bart Van Assche
2018-01-19 7:34 ` Ming Lei
2018-01-19 19:47 ` Bart Van Assche
2018-01-19 19:47 ` Bart Van Assche
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