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Message-ID: <983e5d039dce9de1d32c71d28fd59bbc01c3fee5.camel@infradead.org>
Subject: Re: [PATCH v2 0/2] Adding per-controller timeout support to nvme
From:   David Woodhouse <dwmw2@infradead.org>
To:     Keith Busch <kbusch@kernel.org>, Sagi Grimberg <sagi@grimberg.me>
Cc:     Maximilian Heyne <mheyne@amazon.de>, Amit Shah <aams@amazon.de>,
        Keith Busch <keith.busch@intel.com>, Jens Axboe <axboe@fb.com>,
        Christoph Hellwig <hch@lst.de>,
        James Smart <james.smart@broadcom.com>,
        linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org
Date:   Wed, 24 Apr 2019 22:30:08 +0200
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         <20190424200706.GB15412@localhost.localdomain>
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On Wed, 2019-04-24 at 14:07 -0600, Keith Busch wrote:
> On Wed, Apr 24, 2019 at 09:55:16AM -0700, Sagi Grimberg wrote:
> >=20
> > > As different nvme controllers are connect via different fabrics, some=
 require
> > > different timeout settings than others. This series implements per-co=
ntroller
> > > timeouts in the nvme subsystem which can be set via sysfs.
> >=20
> > How much of a real issue is this?
> >=20
> > block io_timeout defaults to 30 seconds which are considered a universa=
l
> > eternity for pretty much any nvme fabric. Moreover, io_timeout is
> > mutable already on a per-namespace level.
> >=20
> > This leaves the admin_timeout which goes beyond this to 60 seconds...
> >=20
> > Can you describe what exactly are you trying to solve?
>=20
> I think they must have an nvme target that is backed by slow media
> (i.e. non-SSD). If that's the case, I think it may be a better option
> if the target advertises relatively shallow queue depths and/or lower
> MDTS that better aligns to the backing storage capabilies.

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.


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