Re: [PATCH] blk-mq-sched: fix performance regression of mq-deadline

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On 07/03/2017 06:37 AM, Ming Lei wrote:
> When mq-deadline is taken, IOPS of sequential read and
> seqential write is observed more than 20% drop on sata(scsi-mq)
> devices, compared with using 'none' scheduler.
> 
> The reason is that the default nr_requests for scheduler is
> too big for small queuedepth devices, and latency is increased
> much.
> 
> Since the principle of taking 256 requests for mq scheduler
> is based on 128 queue depth, this patch changes into
> double size of min(hw queue_depth, 128).

That's somewhat odd, but it's a better default than some random
value. I'll apply it, thanks Ming.

-- 
Jens Axboe




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