linux-kernel - Re: [PATCH RFC] scsi: core: remove unsed 'restarts' from scsi

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Date:   Sun, 27 Nov 2022 17:45:02 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Yu Kuai <yukuai1@...weicloud.com>
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com,
        linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH RFC] scsi: core: remove unsed 'restarts' from scsi_device

On Sat, Nov 26, 2022 at 04:54:46PM +0800, Yu Kuai wrote:
> Hi,
> 
> 在 2022/11/18 19:30, Yu Kuai 写道:
> > From: Yu Kuai <yukuai3@...wei.com>
> > 
> > During code review, I found that 'restarts' is not useful anymore after
> > the following commits:
> > 
> > 1) commit ab3cee3762e5 ("blk-mq: In blk_mq_dispatch_rq_list() "no budget"
> > is a reason to kick")
> > 2) commit d3b38596875d ("blk-mq: run queue no matter whether the request
> > is the last request")
> > 3) commit 673235f91531 ("scsi: core: Fix race between handling STS_RESOURCE
> > and completion")
> > 
> > Now that if get budget ever failed, block layer will make sure to
> > trigger new run queue for the hctx. Hence there is no need to run queue
> > from scsi layer in this case.
> > 
> 
> Does anyone has suggestions about this patch?
> 
> More info why I tried to remove this:
> 
> while testing megaraid with 4 nvme with none elevator, the default
> queue_depth is 128, while I test it with fio 128 jobs and 1 iodepth,
> bw is about 4Gib/s, however, if I test with 128 jobs and 2 iodepth,
> bw is decreased to about 0.8Gib/s, and with this patch applied,
> bw can stay 4Gib/s in the later case.

I will look at this patch next week.

Can you investigate a bit the reason why perf boost is from this patch?

Thanks,
Ming