From mboxrd@z Thu Jan  1 00:00:00 1970
From: Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH v3 0/8] dm: add request-based blk-mq support
Date: Fri, 02 Jan 2015 18:53:33 +0100
Message-ID: <54A6DB1D.4030201@acm.org>
References: <20141219153801.GA8697@redhat.com>
	<20141219171438.GA6347@redhat.com> <5498389D.6070909@acm.org>
	<20141222184910.GB8054@redhat.com> <54999756.70303@acm.org>
	<1v2g6masssbu88ans1r6lres.1419354811001@email.android.com>
	<CAMM=eLd_A+fRBHDvcDqwF1a9co+G7XZvVhRyBd1AjxOdgjKhbA@mail.gmail.com>
	<549AB979.4050302@acm.org> <20141224182143.GA12922@redhat.com>
	<20141224185529.GA13246@redhat.com>
	<20141224192643.GA30461@redhat.com>
Reply-To: device-mapper development <dm-devel@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <dm-devel-bounces@redhat.com>
In-Reply-To: <20141224192643.GA30461@redhat.com>
List-Unsubscribe: <https://www.redhat.com/mailman/options/dm-devel>,
	<mailto:dm-devel-request@redhat.com?subject=unsubscribe>
List-Archive: <https://www.redhat.com/archives/dm-devel>
List-Post: <mailto:dm-devel@redhat.com>
List-Help: <mailto:dm-devel-request@redhat.com?subject=help>
List-Subscribe: <https://www.redhat.com/mailman/listinfo/dm-devel>,
	<mailto:dm-devel-request@redhat.com?subject=subscribe>
Sender: dm-devel-bounces@redhat.com
Errors-To: dm-devel-bounces@redhat.com
To: Mike Snitzer <snitzer@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>, Christoph Hellwig <hch@infradead.org>, Keith Busch <keith.busch@intel.com>, device-mapper development <dm-devel@redhat.com>, Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
List-Id: dm-devel.ids

On 12/24/14 20:26, Mike Snitzer wrote:
> This fixes it:
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index cdd84e9..138ffb2 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -2030,6 +2030,8 @@ int blk_insert_cloned_request(struct request_queue *q, struct request *rq)
>  		return -EIO;
>  
>  	if (q->mq_ops) {
> +		if (blk_queue_io_stat(rq->q))
> +			blk_account_io_start(rq, true);
>  		blk_mq_insert_request(rq, false, true, true);
>  		return 0;
>  	}
> 
> I've folded this fix into this commit (and rebased the 'for-next' and
> 'dm-for-3.20-blk-mq' branches):
> https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=1fd5e9c83c4ae6a5144783855e9b29a8f42bdc4a

Hello Mike,

Thanks, my tests confirm that this patch indeed fixes the issue I had
reported. Unfortunately this doesn't mean that the blk-mq multipath code
is already working perfectly. Most of the time I/O requests are
processed within the expected time but sometimes I/O processing takes
much more time than what I expected:

# /usr/bin/time -f %e mkfs.xfs -f /dev/dm-0 >/dev/null
0.02
# /usr/bin/time -f %e mkfs.xfs -f /dev/dm-0 >/dev/null
0.02
# /usr/bin/time -f %e mkfs.xfs -f /dev/dm-0 >/dev/null
8.68

However, if I run the same command on the underlying device it always
completes within the expected time.

Bart.