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From: Hannes Reinecke <hare@suse.de>
To: Mike Snitzer <snitzer@redhat.com>, axboe@kernel.dk, dm-devel@redhat.com
Cc: linux-block@vger.kernel.org
Subject: Re: [PATCH 2/3] dm rq: add DM_MAPIO_DELAY_REQUEUE to delay requeue of blk-mq requests
Date: Wed, 14 Sep 2016 08:24:58 +0200	[thread overview]
Message-ID: <1bffba61-1643-54ea-2e8d-a24326bd2381@suse.de> (raw)
In-Reply-To: <1473782495-44128-3-git-send-email-snitzer@redhat.com>

On 09/13/2016 06:01 PM, Mike Snitzer wrote:
> Otherwise blk-mq will immediately dispatch requests that are requeued
> via a BLK_MQ_RQ_QUEUE_BUSY return from blk_mq_ops .queue_rq.
> 
> Delayed requeue is implemented using blk_mq_delay_kick_requeue_list()
> with a delay of 5 secs.  In the context of DM multipath (all paths down)
> it doesn't make any sense to requeue more quickly.
> 
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>  drivers/md/dm-rq.c            | 35 ++++++++++++++++++++---------------
>  include/linux/device-mapper.h |  1 +
>  2 files changed, 21 insertions(+), 15 deletions(-)
> 
Hmm. Not sure if I agree with the reasoning for a 5 seconds delay; this
seems to be a rather broad estimate.
Won't it delay I/O resumption when we have intermittent path failure (eg
on iSCSI)?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 N�rnberg
GF: J. Hawn, J. Guild, F. Imend�rffer, HRB 16746 (AG N�rnberg)

WARNING: multiple messages have this Message-ID (diff)
From: Hannes Reinecke <hare@suse.de>
To: Mike Snitzer <snitzer@redhat.com>, axboe@kernel.dk, dm-devel@redhat.com
Cc: linux-block@vger.kernel.org
Subject: Re: [PATCH 2/3] dm rq: add DM_MAPIO_DELAY_REQUEUE to delay requeue of blk-mq requests
Date: Wed, 14 Sep 2016 08:24:58 +0200	[thread overview]
Message-ID: <1bffba61-1643-54ea-2e8d-a24326bd2381@suse.de> (raw)
In-Reply-To: <1473782495-44128-3-git-send-email-snitzer@redhat.com>

On 09/13/2016 06:01 PM, Mike Snitzer wrote:
> Otherwise blk-mq will immediately dispatch requests that are requeued
> via a BLK_MQ_RQ_QUEUE_BUSY return from blk_mq_ops .queue_rq.
> 
> Delayed requeue is implemented using blk_mq_delay_kick_requeue_list()
> with a delay of 5 secs.  In the context of DM multipath (all paths down)
> it doesn't make any sense to requeue more quickly.
> 
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
> ---
>  drivers/md/dm-rq.c            | 35 ++++++++++++++++++++---------------
>  include/linux/device-mapper.h |  1 +
>  2 files changed, 21 insertions(+), 15 deletions(-)
> 
Hmm. Not sure if I agree with the reasoning for a 5 seconds delay; this
seems to be a rather broad estimate.
Won't it delay I/O resumption when we have intermittent path failure (eg
on iSCSI)?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)

  reply	other threads:[~2016-09-14  6:24 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-09-13 16:01 [PATCH for-4.9 0/3] allow delayed requeue of blk-mq requests Mike Snitzer
2016-09-13 16:01 ` [PATCH 1/3] blk-mq: introduce blk_mq_delay_kick_requeue_list() Mike Snitzer
2016-09-14  6:22   ` Hannes Reinecke
2016-09-14  6:22     ` Hannes Reinecke
2016-09-14 11:28   ` Bart Van Assche
2016-09-14 13:45     ` Mike Snitzer
2016-09-14 15:04   ` Jens Axboe
2016-09-14 15:13     ` Mike Snitzer
2016-09-13 16:01 ` [PATCH 2/3] dm rq: add DM_MAPIO_DELAY_REQUEUE to delay requeue of blk-mq requests Mike Snitzer
2016-09-14  6:24   ` Hannes Reinecke [this message]
2016-09-14  6:24     ` Hannes Reinecke
2016-09-14 13:51     ` Mike Snitzer
2016-09-13 16:01 ` [PATCH 3/3] dm mpath: delay the requeue of blk-mq requests while all paths down Mike Snitzer
2016-09-14  6:25   ` Hannes Reinecke
2016-09-14  6:25     ` Hannes Reinecke

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