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

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Date:   Mon, 28 Nov 2022 11:35:18 +0800
From:   Yu Kuai <yukuai1@...weicloud.com>
To:     Ming Lei <ming.lei@...hat.com>, 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



在 2022/11/28 11:27, Ming Lei 写道:
> 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.
>>>
> 
> But scsi_run_queue_async() needs to run all hw queue because budget is
> actually LUN/request queue wide.

Why the hw queue need to run if get budget never failed in this hw
queue?

> 
>>
>> 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?
test cmd:
fio -name=0 -ioengine=libaio -direct=1 -group_reporting=1 -randseed=2022 
-rwmixread=70 -refill_buffers -filename=/dev/sdg -numjobs=128 -size=1TB 
-runtime=60s -bs=4k -iodepth=2 -rw=randwrite

test environment:
arm64 Kunpeng-920, 128 cpu
megaraid with 4 NVMEs, 128 hctx and queue_depth is 128

> 
> 
> 
> thanks,
> Ming
> 
> .
>