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Date:   Mon, 28 Nov 2022 11:27:49 +0800
From:   Ming Lei <ming.lei@redhat.com>
To:     Yu Kuai <yukuai1@huaweicloud.com>
Cc:     jejb@linux.ibm.com, martin.petersen@oracle.com,
        linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, "yukuai (C)" <yukuai3@huawei.com>
Subject: Re: [PATCH RFC] scsi: core: remove unsed 'restarts' from scsi_device
Message-ID: <Y4QqtbXsuYmkOe88@T590>
References: <20221118113052.1324140-1-yukuai1@huaweicloud.com>
 <cefdae2e-67e3-b4b4-f569-31db960e991f@huaweicloud.com>
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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@huawei.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.
> > 

But scsi_run_queue_async() needs to run all hw queue because budget is
actually LUN/request queue wide.

> 
> 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.

What is .can_queue and nr_hw_queues in your setting?


thanks,
Ming