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Message-ID: <aef69f3b-a8db-f34c-4a52-49ba9020f6cf@huaweicloud.com> Date: Sat, 26 Nov 2022 14:08:02 +0800 From: Yu Kuai <yukuai1@...weicloud.com> To: Ming Lei <ming.lei@...hat.com>, Yu Kuai <yukuai1@...weicloud.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? 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? > > 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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