Re: [PATCH V13 00/10] mmc: Add Command Queue support

From: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
To: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ulf Hansson <ulf.hansson@linaro.org>,
	linux-mmc <linux-mmc@vger.kernel.org>,
	linux-block <linux-block@vger.kernel.org>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	Bough Chen <haibo.chen@nxp.com>,
	Alex Lemberg <alex.lemberg@sandisk.com>,
	Mateusz Nowak <mateusz.nowak@intel.com>,
	Yuliy Izrailov <Yuliy.Izrailov@sandisk.com>,
	Jaehoon Chung <jh80.chung@samsung.com>,
	Dong Aisheng <dongas86@gmail.com>,
	Das Asutosh <asutoshd@codeaurora.org>,
	Zhangfei Gao <zhangfei.gao@gmail.com>,
	Sahitya Tummala <stummala@codeaurora.org>,
	Harjani Ritesh <riteshh@codeaurora.org>,
	Venu Byravarasu <vbyravarasu@nvidia.com>,
	Linus Walleij <linus.walleij@linaro.org>,
	Shawn Lin <shawn.lin@rock-chips.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [PATCH V13 00/10] mmc: Add Command Queue support
Date: Thu, 16 Nov 2017 10:46:40 +0100	[thread overview]
Message-ID: <1716036.6EalJ2kXtr@amdc3058> (raw)
In-Reply-To: <1509715220-31885-1-git-send-email-adrian.hunter@intel.com>

On Friday, November 03, 2017 03:20:10 PM Adrian Hunter wrote:
> Hi
> 
> Here is V13 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.

Tested-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com> [ for non-CQE changes ]

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics