linux-kernel - Re: [PATCH v4 1/2] nvme: add tracepoint for nvme_setup

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Date:   Mon, 22 Jan 2018 16:59:56 +0100
From:   Christoph Hellwig <hch@....de>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     Christoph Hellwig <hch@....de>, Sagi Grimberg <sagi@...mberg.me>,
        Keith Busch <keith.busch@...el.com>,
        Linux Kernel Mailinglist <linux-kernel@...r.kernel.org>,
        Hannes Reinecke <hare@...e.de>,
        Linux NVMe Mailinglist <linux-nvme@...ts.infradead.org>,
        "Martin K . Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v4 1/2] nvme: add tracepoint for nvme_setup_cmd

On Mon, Jan 22, 2018 at 04:53:56PM +0100, Johannes Thumshirn wrote:
> Yes and no. I personally like to have the big hammer when tracing customer
> problems and filter out maunally later. I initially had a tracepoint for each
> of nvme_setup_flush(), nvme_setup_discard(), nvme_setup_rw() but decided it
> was too fine grained.
> 
> nvme_setup_cmd() has the nice side effect that all commands, including
> userspace passtrough commands must pass it. This was extremely helpful in the
> customer bug which inspired me to implement this tracepoint.

Not arguing against placing the tracepoint(s) in nvme_setup_cmd, but
it seems like we should have one for admin and one for I/O commands.
Especially as we have to special case them just about everywhere,
and the overlap of the opcode space is pretty annoying.