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Date:   Fri, 3 May 2019 06:12:32 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Akinobu Mita <akinobu.mita@gmail.com>
Cc:     Keith Busch <keith.busch@intel.com>,
        linux-nvme@lists.infradead.org,
        LKML <linux-kernel@vger.kernel.org>,
        Johannes Berg <johannes@sipsolutions.net>,
        Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 0/4] nvme-pci: support device coredump
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On Fri, May 03, 2019 at 12:38:08PM +0900, Akinobu Mita wrote:
> 2019年5月2日(木) 22:03 Keith Busch <keith.busch@intel.com>:
> > On Thu, May 02, 2019 at 05:59:17PM +0900, Akinobu Mita wrote:
> > > This enables to capture snapshot of controller information via device
> > > coredump machanism, and it helps diagnose and debug issues.
> > >
> > > The nvme device coredump is triggered before resetting the controller
> > > caused by I/O timeout, and creates the following coredump files.
> > >
> > > - regs: NVMe controller registers, including each I/O queue doorbell
> > >         registers, in nvme-show-regs style text format.
> >
> > You're supposed to treat queue doorbells as write-only. Spec says:
> >
> >   The host should not read the doorbell registers. If a doorbell register
> >   is read, the value returned is vendor specific.
> 
> OK.  I'll exclude the doorbell registers from register dump.  It will work
> out without the information if we have snapshot of the queues.

Could you actually explain how the rest is useful? I personally have
never encountered an issue where knowing these values would have helped:
every device timeout always needed device specific internal firmware
logs in my experience.