linux-kernel - Re: scsi-mq

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Date:	Tue, 17 Jun 2014 16:27:52 +0200
From:	Bart Van Assche <bvanassche@....org>
To:	Christoph Hellwig <hch@....de>,
	James Bottomley <James.Bottomley@...senPartnership.com>
CC:	Jens Axboe <axboe@...nel.dk>,
	Bart Van Assche <bvanassche@...ionio.com>,
	Robert Elliot <Elliott@...com>, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: scsi-mq

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.

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

Bart.
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