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

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Message-ID: <20190424200706.GB15412@localhost.localdomain>
Date:   Wed, 24 Apr 2019 14:07:06 -0600
From:   Keith Busch <kbusch@...nel.org>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Maximilian Heyne <mheyne@...zon.de>,
        David Woodhouse <dwmw2@...radead.org>,
        Amit Shah <aams@...zon.de>,
        Keith Busch <keith.busch@...el.com>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>,
        James Smart <james.smart@...adcom.com>,
        linux-nvme@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 0/2] Adding per-controller timeout support to nvme

On Wed, Apr 24, 2019 at 09:55:16AM -0700, Sagi Grimberg wrote:
> 
> > As different nvme controllers are connect via different fabrics, some require
> > different timeout settings than others. This series implements per-controller
> > timeouts in the nvme subsystem which can be set via sysfs.
> 
> How much of a real issue is this?
> 
> block io_timeout defaults to 30 seconds which are considered a universal
> eternity for pretty much any nvme fabric. Moreover, io_timeout is
> mutable already on a per-namespace level.
> 
> This leaves the admin_timeout which goes beyond this to 60 seconds...
> 
> Can you describe what exactly are you trying to solve?

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.