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Message-ID: <7fa1cf9f-3cd3-9ca8-8ddc-0c8407a466e8@huaweicloud.com> Date: Sat, 26 Nov 2022 14:08:56 +0800 From: Yu Kuai <yukuai1@...weicloud.com> To: Yu Kuai <yukuai1@...weicloud.com>, Ming Lei <ming.lei@...hat.com> Cc: John Garry <john.g.garry@...cle.com>, kashyap.desai@...adcom.com, sumit.saxena@...adcom.com, shivasharan.srikanteshwara@...adcom.com, jejb@...ux.ibm.com, martin.petersen@...cle.com, megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org, linux-block <linux-block@...r.kernel.org>, "zhangyi (F)" <yi.zhang@...wei.com>, "yukuai (C)" <yukuai3@...wei.com> Subject: Re: Why is MEGASAS_SAS_QD set to 256? 在 2022/11/26 14:08, Yu Kuai 写道: > Hi, Ming > > 在 2022/11/26 10:18, Ming Lei 写道: >> >> If you want aggressive merge on sequential IO workload, the queue >> depth need >> to be a bit less, then more requests can be staggered into scheduler >> queue, >> and merge chance is increased. > > But if nr_requests >= queue_depth, it seems to me elevator will have no > effect, no request can be merged or sorted by scheduler, right? Sorry that should be nr_requests <= queue_depth. >> >> If you want good perf on random IO perf, the queue depth needs to >> be deep enough to have enough parallelism for saturating SSD internal. >> >> But we don't recognize sequential/random IO pattern, and usually fixed >> queue depth is used. > > Is it possible to use none elevator and set large queue_depth if nvme is > used in this case? > > Thansk, > Kuai >> >> Thanks, >> Ming >> >> . >> > > . >
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