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Date: Wed, 22 May 2019 14:28:05 -0600
From: Keith Busch <kbusch@kernel.org>
To: Bart Van Assche <bvanassche@acm.org>
Cc: Keith Busch <keith.busch@intel.com>, Jens Axboe <axboe@kernel.dk>,
Christoph Hellwig <hch@lst.de>, linux-nvme@lists.infradead.org,
linux-block@vger.kernel.org, Ming Lei <ming.lei@redhat.com>
Subject: Re: [PATCH 0/2] Reset timeout for paused hardware
Message-ID: <20190522202805.GA5781@localhost.localdomain>
References: <20190522174812.5597-1-keith.busch@intel.com>
<721e059e-ed88-734c-fea2-3637e6d31f4c@acm.org>
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On Wed, May 22, 2019 at 10:20:45PM +0200, Bart Van Assche wrote:
> On 5/22/19 7:48 PM, Keith Busch wrote:
> > Hardware may temporarily stop processing commands that have
> > been dispatched to it while activating new firmware. Some target
> > implementation's paused state time exceeds the default request expiry,
> > so any request dispatched before the driver could quiesce for the
> > hardware's paused state will time out, and handling this may interrupt
> > the firmware activation.
> >
> > This two-part series provides a way for drivers to reset dispatched
> > requests' timeout deadline, then uses this new mechanism from the nvme
> > driver's fw activation work.
>
> Hi Keith,
>
> Is it essential to modify the block layer to implement this behavior
> change? Would it be possible to implement this behavior change by
> modifying the NVMe driver only, e.g. by modifying the nvme_timeout()
> function and by making that function return BLK_EH_RESET_TIMER while new
> firmware is being activated?
Good question.
We can't just do this from nvme_timeout(), though. That introduces races
between timeout_work and fw_act_work if that fw work clears the
condition that timeout needs to observe to return RESET_TIMER.
Even if we avoid that race, the rq->deadline needs to be adjusted to
the current time after the h/w unpause because the time accumulated while
h/w halted itself should not be counted against the request.