linux-kernel - Re: [RESEND PATCH v1 1/2] trace: events: scsi: Add tag in SCSI trace events

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Date:   Tue, 17 Apr 2018 12:09:26 +0000
From:   "Bean Huo (beanhuo)" <beanhuo@...ron.com>
To:     Bart Van Assche <Bart.VanAssche@....com>,
        "rostedt@...dmis.org" <rostedt@...dmis.org>,
        "rajatja@...gle.com" <rajatja@...gle.com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...had.com" <mingo@...had.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "jejb@...ux.vnet.ibm.com" <jejb@...ux.vnet.ibm.com>
Subject: Re: [RESEND PATCH v1 1/2] trace: events: scsi: Add tag in SCSI trace
 events

>On Mon, 2018-04-16 at 20:27 +0000, Bean Huo (beanhuo) wrote:
>> By the way, these patches are not to add new feature, they are just to
>> add print tag along with the other exist printed request parameters.
>
>Are you aware that there are two tag fields in struct request, namely "tag"
>and "internal_tag"? Are you aware that how these fields are used depends on
>whether or not a scheduler is attached to a request queue? Have you verified
>that the "tag" field contains a meaningful value for blk-mq for every blk-mq
>tracepoint?
>
>Thanks,
>
>Bart.
>
>
Yes, I noticed and was aware, there are tag and internal_tag.
One thing I was not aware is that the patches would make such a big impact on blk-mq based on
Your comments.

I am not expert on block layer, that is why I added block maintainer here.
Please point out which line and what is problem? If there is some wrong with the patch.
Which one is correct "tag" to track request? 

Thanks,
//Bean Huo