linux-kernel - Re: [PATCH 2/2] ufs: don't use the fair tag sharings

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Message-ID: <097caed2-10b3-7cd1-7c06-90f983e5c720@acm.org>
Date:   Wed, 17 May 2023 11:23:13 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Yu Kuai <yukuai1@...weicloud.com>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Ed Tsai <ed.tsai@...iatek.com>, axboe@...nel.dk,
        linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, martin.petersen@...cle.com,
        stanley.chu@...iatek.com, peter.wang@...iatek.com,
        chun-hung.wu@...iatek.com, alice.chao@...iatek.com,
        powen.kao@...iatek.com, naomi.chu@...iatek.com,
        wsd_upstream@...iatek.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH 2/2] ufs: don't use the fair tag sharings

On 5/17/23 00:49, Yu Kuai wrote:
> 在 2023/05/16 23:12, Bart Van Assche 写道:
>> I propose that we switch to one of these two approaches:
> 
> How about a smoothing method that the device with more io will share
> more tag, and each device will get at least one tag?

Hi Yu,

hctx_may_queue() is called from the hot path (blk_mq_get_tag()). I'm 
pretty sure that adding any nontrivial code in that path will cause a 
performance (IOPS) regression. So I don't think that adding a smoothing 
method in hctx_may_queue() is a realistic option.

Thanks,

Bart.