linux-kernel - Re: [PATCH v2 1/3] scsi: ufs: core: Introduce mcq ops to config cqid

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Date:   Wed, 31 May 2023 05:48:27 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Stanley Chu <chu.stanley@...il.com>
Cc:     Po-Wen Kao <powen.kao@...iatek.com>, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        wsd_upstream@...iatek.com, peter.wang@...iatek.com,
        stanley.chu@...iatek.com, alice.chao@...iatek.com,
        naomi.chu@...iatek.com, chun-hung.wu@...iatek.com,
        cc.chou@...iatek.com, eddie.huang@...iatek.com
Subject: Re: [PATCH v2 1/3] scsi: ufs: core: Introduce mcq ops to config cqid

On 5/30/23 18:54, Stanley Chu wrote:
> In addition, some benchmark data shows that the performance can be
> improved by using fewer CQs to aggregate the interrupt handling of
> completion requests.

What has been measured? IOPS only or both IOPS and latency?

How big is the difference? A few percent or more?

For which number of SQs and which number of CQs has performance data 
been measured?

Would the following work instead of introducing a new vop?
- Introduce a new capability flag, e.g. UFSHCD_CAP_SINGLE_CQ.
- Set that flag from inside ufs_mtk_init().
- Modify the UFS core driver such that the number of completion queues
   depends on the UFSHCD_CAP_SINGLE_CQ flag.

> Therefore, we would like to introduce a vop to allow the host to
> configure it accordingly.

We do not accept new vops upstream without a user. Where is the 
implementation of the new .config_cqid() callback?

Thanks,

Bart.