linux-kernel - Re: [PATCH v2 1/1] scsi: ufs: core: Make UFS_MCQ_NUM_DEV_CMD

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Message-ID: <ecd8d769-4143-550c-13b5-ae96e6a76ff6@acm.org>
Date:   Tue, 30 May 2023 16:50:53 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     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>
Cc:     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 1/1] scsi: ufs: core: Make UFS_MCQ_NUM_DEV_CMD_QUEUES a
 module parameter

On 5/29/23 19:35, Po-Wen Kao wrote:
> A dedicated queue for dev commands is not mandatory, hence let
> UFS_MCQ_NUM_DEV_CMD_QUEUES become module parameter `dev_cmd_queues`
> to allow sharing first hw queue for dev commands.
> 
> When `dev_cmd_queues` is set to 0, the hwq 0 will be shared for I/O
> requests and dev commands. In the same hwq, commands are processed based
> on submission order hence might take longer to dispatch dev command
> under heavy traffic. For the host with dedicated hwq for dev commands
> can benefit in such scenario.

The UFS core has already too many kernel module parameters. I don't 
think that we need more kernel module parameters. Instead of adding a 
new kernel module parameter, I propose to never reserve a hardware queue 
for device commands. Reserving a hardware queue for device commands 
seems wasteful to me.

Thanks,

Bart.