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

From: Bartlomiej Zolnierkiewicz
Date: Thu Nov 16 2017 - 04:47:07 EST


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@xxxxxxxxxxx> [ for non-CQE changes ]

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