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

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Date:   Tue, 28 Mar 2023 20:17:19 -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,
        mason.zhang@...iatek.com, chaotian.jing@...iatek.com,
        jiajie.hao@...iatek.com
Subject: Re: [PATCH] scsi: ufs: core: Make UFS_MCQ_NUM_DEV_CMD_QUEUES a module
 parameter

On 3/28/23 03:29, 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.

Which queue is selected for device management commands?

What is the impact of this change? If a device command is queued on a 
queue with multiple pending commands, does that mean that it can take 
long for the device command to reach the UFS device?

The answer to the above questions should be in the patch description. 
Please expand the patch description.

> +unsigned int dev_cmd_queues = 1;
> +module_param_cb(dev_cmd_queues, &dev_cmd_queue_count_ops, &dev_cmd_queues, 0644);
> +MODULE_PARM_DESC(dev_cmd_queues,
> +		 "Number of queues used for dev command. Default value is 1");

I prefer a solution that does not require any new kernel module 
parameters. That means either a dedicated device command queue for all 
host controllers or no dedicated device command queue for any host 
controller.

Thanks,

Bart.