linux-kernel - Re: Block Layer Multi queue question

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Date:	Thu, 27 Jun 2013 16:21:27 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	xun ni <ni.xun.intel@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Block Layer Multi queue question

On Thu, Jun 27 2013, xun ni wrote:
> Hello, Axboe:
> 
>    I read your article about the block io layer Multi-queue support SSD on
> the multi-core systems. And i do some experiment on raid5 which consist of
> 5 intel ssd disks. I get code from linux-block and checked out mq. After
> apply kent's patch , the raid5 system works. I tested the raid with FIO and
> find that the performance is not growing. 4k read iops down from 82k to
> 76k. 4k random write iops down from 14k to 9k. The latency is also down
> about 8%
>    So my question is that any configuration or modification is needed
> before testing the raid5 so that the Multi-queue method works and
> performance increase?

raid5/md isn't blk-mq aware at all. So that code path isn't really
changed at all. If you are seeing a change in performance, that must be
because the baseline is different (blk-mq sits on top of 3.10-rc, don't
know what you are comparing to). You should try 3.10-rc7 and see how
that fares, and report if you are seeing a performance degredation.

-- 
Jens Axboe

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