linux-kernel - Re: [PATCH RESEND] scsi: megaraid_sas: make module parameter scmd

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Date: Mon, 8 Apr 2024 13:30:07 +0100
From: John Garry <john.g.garry@...cle.com>
To: Lei Chen <lei.chen@...rtx.com>,
        Kashyap Desai
 <kashyap.desai@...adcom.com>,
        Sumit Saxena <sumit.saxena@...adcom.com>,
        Shivasharan S <shivasharan.srikanteshwara@...adcom.com>,
        Chandrakanth patil <chandrakanth.patil@...adcom.com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>
Cc: megaraidlinux.pdl@...adcom.com, linux-scsi@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RESEND] scsi: megaraid_sas: make module parameter
 scmd_timeout writable

On 08/04/2024 11:05, Lei Chen wrote:
> When an scmd times out, block layer calls megasas_reset_timer to
> make further decisions. scmd_timeout indicates when an scmd is really
> timed-out.

What does really timed-out mean?

> If we want to make this process more fast, we can decrease
> this value. This patch allows users to change this value in run-time.
> 
> Signed-off-by: Lei Chen <lei.chen@...rtx.com>
> ---
>   drivers/scsi/megaraid/megaraid_sas_base.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/scsi/megaraid/megaraid_sas_base.c b/drivers/scsi/megaraid/megaraid_sas_base.c
> index 3d4f13da1ae8..2a165e5dc7a3 100644
> --- a/drivers/scsi/megaraid/megaraid_sas_base.c
> +++ b/drivers/scsi/megaraid/megaraid_sas_base.c
> @@ -91,7 +91,7 @@ module_param(dual_qdepth_disable, int, 0444);
>   MODULE_PARM_DESC(dual_qdepth_disable, "Disable dual queue depth feature. Default: 0");
>   
>   static unsigned int scmd_timeout = MEGASAS_DEFAULT_CMD_TIMEOUT;
> -module_param(scmd_timeout, int, 0444);
> +module_param(scmd_timeout, int, 0644);
>   MODULE_PARM_DESC(scmd_timeout, "scsi command timeout (10-90s), default 90s. See megasas_reset_timer.");
>   
>   int perf_mode = -1;

I don't know why megaraid_sas has special handling here (and bypasses 
SCSI midlayer).

If the host is overloaded and you get a time-out as a command simply 
could not be handled in time, can you alternatively try reducing the 
scsi device queue depth?