linux-kernel - Re: [PATCH V9 00/15] mmc: Add Command Queue support

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Date:   Wed, 11 Oct 2017 15:24:37 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Adrian Hunter <adrian.hunter@...el.com>
Cc:     linux-mmc <linux-mmc@...r.kernel.org>,
        linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Bough Chen <haibo.chen@....com>,
        Alex Lemberg <alex.lemberg@...disk.com>,
        Mateusz Nowak <mateusz.nowak@...el.com>,
        Yuliy Izrailov <Yuliy.Izrailov@...disk.com>,
        Jaehoon Chung <jh80.chung@...sung.com>,
        Dong Aisheng <dongas86@...il.com>,
        Das Asutosh <asutoshd@...eaurora.org>,
        Zhangfei Gao <zhangfei.gao@...il.com>,
        Sahitya Tummala <stummala@...eaurora.org>,
        Harjani Ritesh <riteshh@...eaurora.org>,
        Venu Byravarasu <vbyravarasu@...dia.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH V9 00/15] mmc: Add Command Queue support

On 27 September 2017 at 00:25, Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On 22 September 2017 at 14:36, Adrian Hunter <adrian.hunter@...el.com> wrote:
>> Hi
>>
>> Here is V9 of the hardware command queue patches without the software
>> command queue patches, now using blk-mq and now with blk-mq support for
>> non-CQE I/O.
>>
>> HW CMDQ offers 25% - 50% better random multi-threaded I/O.  I see a slight
>> 2% drop in sequential read speed but no change to sequential write.
>>
>> Non-CQE blk-mq showed a 3% decrease in sequential read performance.  This
>> seemed to be coming from the inferior latency of running work items compared
>> with a dedicated thread.  Hacking blk-mq workqueue to be unbound reduced the
>> performance degradation from 3% to 1%.
>>
>> While we should look at changing blk-mq to give better workqueue performance,
>> a bigger gain is likely to be made by adding a new host API to enable the
>> next already-prepared request to be issued directly from within ->done()
>> callback of the current request.
>
> I have looked at patch 1->8, and those looks nice to me so I have
> applied those for next. I will do my best to review the rest asap,
> however I am currently traveling so in worst case it will have wait
> until next week.

Adrian, I decided to drop patch6, the one which adds the Kconfig
option for blkmq for now. Please re-post it when you get to the point
of sending a version of the series.

Kind regards
Uffe