From mboxrd@z Thu Jan  1 00:00:00 1970
From: hch@lst.de (Christoph Hellwig)
Date: Mon, 12 Oct 2015 22:22:17 +0200
Subject: [PATCH, RFC] blk-mq: use a delayed work item for timeouts
In-Reply-To: <561C1324.3030800@fb.com>
References: <1444678154-24766-1-git-send-email-hch@lst.de>
 <561C0B3C.70004@fb.com> <561C1324.3030800@fb.com>
Message-ID: <20151012202217.GA880@lst.de>

On Mon, Oct 12, 2015@02:08:04PM -0600, Jens Axboe wrote:
>> No that's definitely fine with me, imho most error handling callbacks
>> should be in process context for ease of use in the driver.
>
> Took a closer look. The patch looks incomplete. The hot path for blk-mq is 
> blk_add_timer(), looks like you left that one alone in the conversion?

Oh, damn.  I had that part in my initial version that also crudely
converted the old request code and dropped a bit too much.  That should
defintively do the queue_deayed_work.

> Might be easier to just leave the timer alone, and if it actually fires 
> _and_ we have to do something, punt to a workqueue instead of invoking the 
> timeout handler directly.

queue_delayed_work just assigns two additional fields, then sets
timer->experies and does an add_timer.  So it's the generic implementation
of your above scheme.  I'd much rather use the generic version if
possible instead of trying to recreate it.