linux-kernel - Re: [PATCH v2 0/2] Adding per-controller timeout support to nvme

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Message-ID: <20190424204417.GC15412@localhost.localdomain>
Date:   Wed, 24 Apr 2019 14:44:17 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     David Woodhouse <dwmw2@...radead.org>
Cc:     Sagi Grimberg <sagi@...mberg.me>, Jens Axboe <axboe@...com>,
        James Smart <james.smart@...adcom.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Keith Busch <keith.busch@...el.com>,
        Maximilian Heyne <mheyne@...zon.de>,
        Amit Shah <aams@...zon.de>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2 0/2] Adding per-controller timeout support to nvme

On Wed, Apr 24, 2019 at 10:30:08PM +0200, David Woodhouse wrote:
> It isn't that the media is slow; the max timeout is based on the SLA
> for certain classes of "fabric" outages. Linux copes *really* badly
> with I/O errors, and if we can make the timeout last long enough to
> cover the switch restart worst case, then users are a lot happier.

Gotchya. So the default timeout is sufficient under normal operation,
but temporary intermittent outages may exceed it. It'd be a real
dissappointment if the command times out with an error anyway after
waiting for the extended time, but we ought to cover the worst case
time for a successful completion.