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From: Jens Axboe <axboe@kernel.dk>
To: Bart Van Assche <bvanassche@acm.org>,
	Christoph Hellwig <hch@lst.de>,
	James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Bart Van Assche <bvanassche@fusionio.com>,
	Robert Elliot <Elliott@hp.com>,
	linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: scsi-mq
Date: Tue, 17 Jun 2014 20:44:58 -0700	[thread overview]
Message-ID: <53A10B3A.6050705@kernel.dk> (raw)
In-Reply-To: <53A05068.4080702@acm.org>

On 2014-06-17 07:27, Bart Van Assche wrote:
> On 06/12/14 15:48, Christoph Hellwig wrote:
>> Bart and Robert have helped with some very detailed measurements that they
>> might be able to send in reply to this, although these usually involve
>> significantly reworked low level drivers to avoid other bottle necks.
>
> In case someone would like to see the results of the measurements I ran,
> these results can be found here:
> https://docs.google.com/file/d/0B1YQOreL3_FxUXFMSjhmNDBNNTg.
>
> Two important conclusions from the data in that PDF document are as follows:
> - A small but significant performance improvement for the traditional
>    SCSI mid-layer (use_blk_mq=N).
> - A very significant performance improvement for multithreaded
>    workloads with use_blk_mq=Y. As an example, the number of I/O
>    operations per second reported for the random write test increased
>    with 170%. That means 2.7 times the performance
>    of use_blk_mq=N.

Thanks for posting these numbers, Bart. The CPU utilization and IOPS 
speak a very clear message. The only mystery is why the singe threaded 
performance is down. That we need to get sort, but it's not a show 
stopper for inclusion.

If you run the single threaded tests and watch for queue depths, is 
there a difference between blk-mq=y/scsi-mq and the stock kernel?

> I think this means the scsi-mq patches are ready for wider use.

I would agree. James, I haven't seen any comments from you on this yet. 
I've run various bits of scsi-mq testing as well, and no ill effects 
seen. On top of that, Christophs patches are nicely separated and have 
general benefits even for the non-blk-mq cases. Time to shove them into 
the queue for the next merge window?

-- 
Jens Axboe


  reply	other threads:[~2014-06-18  3:45 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-12 13:48 scsi-mq Christoph Hellwig
2014-06-12 13:48 ` [PATCH 01/14] sd: don't use rq->cmd_len before setting it up Christoph Hellwig
2014-06-12 13:48 ` [PATCH 02/14] scsi: split __scsi_queue_insert Christoph Hellwig
2014-06-12 13:48 ` [PATCH 03/14] scsi: centralize command re-queueing in scsi_dispatch_fn Christoph Hellwig
2014-06-12 13:48 ` [PATCH 04/14] scsi: set ->scsi_done before calling scsi_dispatch_cmd Christoph Hellwig
2014-06-12 13:48 ` [PATCH 05/14] scsi: push host_lock down into scsi_{host,target}_queue_ready Christoph Hellwig
2014-06-12 13:48 ` [PATCH 06/14] scsi: convert target_busy to an atomic_t Christoph Hellwig
2014-06-12 13:48 ` [PATCH 07/14] scsi: convert host_busy to atomic_t Christoph Hellwig
2014-06-12 13:49 ` [PATCH 08/14] scsi: convert device_busy " Christoph Hellwig
2014-06-12 13:49 ` [PATCH 09/14] scsi: fix the {host,target,device}_blocked counter mess Christoph Hellwig
2014-06-12 13:49 ` [PATCH 10/14] scsi: only maintain target_blocked if the driver has a target queue limit Christoph Hellwig
2014-06-21 22:10   ` Elliott, Robert (Server Storage)
2014-06-23  7:09     ` Christoph Hellwig
2014-06-12 13:49 ` [PATCH 11/14] scsi: unwind blk_end_request_all and blk_end_request_err calls Christoph Hellwig
2014-06-12 13:49 ` [PATCH 12/14] scatterlist: allow chaining to preallocated chunks Christoph Hellwig
2014-06-12 13:49 ` [PATCH 13/14] scsi: add support for a blk-mq based I/O path Christoph Hellwig
2014-06-12 13:49 ` [PATCH 14/14] fnic: reject device resets without assigned tags for the blk-mq case Christoph Hellwig
2014-06-13  6:42 ` scsi-mq Bart Van Assche
2014-06-17 14:27 ` scsi-mq Bart Van Assche
2014-06-18  3:44   ` Jens Axboe [this message]
2014-06-18  7:09     ` scsi-mq Bart Van Assche
2014-06-21  0:52       ` scsi-mq Elliott, Robert (Server Storage)
2014-06-23  7:09         ` scsi-mq Christoph Hellwig
2014-06-19  0:58     ` scsi-mq Elliott, Robert (Server Storage)

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