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

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Date:   Sat, 26 Nov 2022 16:54:46 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Yu Kuai <yukuai1@...weicloud.com>, ming.lei@...hat.com,
        jejb@...ux.ibm.com, martin.petersen@...cle.com
Cc:     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

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.

Thanks,
Kuai