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

[Bartlomiej Zolnierkiewicz]

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