linux-kernel - Re: [PATCH] scsi: core: Log SCSI command age with errors

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Message-ID: <31eb5bb6-ca4e-1c6c-3013-7d94ff49623d@redhat.com>
Date:   Mon, 30 Sep 2019 14:35:45 +0530
From:   "Milan P. Gandhi" <mgandhi@...hat.com>
To:     Martin Wilck <mwilck@...e.de>,
        Laurence Oberman <loberman@...hat.com>,
        linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Cc:     jejb@...ux.ibm.com, martin.petersen@...cle.com
Subject: Re: [PATCH] scsi: core: Log SCSI command age with errors

On 9/30/19 2:12 PM, Martin Wilck wrote:
> On Fri, 2019-09-27 at 13:45 -0400, Laurence Oberman wrote:
>>
>> Hi Martin
>>
>> Agreed about log extraction, but turning that on with a busy workload
>> in a production environment is not practical. We cant do it with
>> systems with 1000's of luns and 1000's of IOPS/sec.
>> Also second resolution is good enough for the debug we want to see.
> 
> I gather that you look at a specific problem where second resolution is
> sufficient. For upstream, the generic usefulness should be considered,
> and I don't think we can say today that better-than-second resolution
> will never be useful, so I still vote for milliseconds.

Ok, I will change it to ms.

> Wrt the enablement of the option on highly loaded systems, I'm not sure
> I understand. You need to enable SCSI logging anyway, don't you?

By default we keep the SCSI debug logging disabled or am I missing 
something?

>Is it an issue to have to set 2 sysfs values rather than just one?

The idea here is to capture the above debug data even without 
any user interventions to change any sysfs entries or to enable 
debug logging on busy, critical production systems.

Also, we are not changing the existing text in SCSI command error log,
but we are only adding one single word at the end of message. Ideally
the user scripts are written to grep specific pattern from the logs.
Since we are not replacing any existing text from the logs, the 
scripts should still work with this change as well.

Thanks,
Milan.