linux-kernel - Re: [PATCH 05/10] block: remove per-queue plugging

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Message-ID: <4DA48AC5.30007@fusionio.com>
Date:	Tue, 12 Apr 2011 19:24:21 +0200
From:	Jens Axboe <jaxboe@...ionio.com>
To:	"hch@...radead.org" <hch@...radead.org>
CC:	Dave Chinner <david@...morbit.com>, NeilBrown <neilb@...e.de>,
	Mike Snitzer <snitzer@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dm-devel@...hat.com" <dm-devel@...hat.com>,
	"linux-raid@...r.kernel.org" <linux-raid@...r.kernel.org>
Subject: Re: [PATCH 05/10] block: remove per-queue plugging

On 2011-04-12 18:54, hch@...radead.org wrote:
> On Tue, Apr 12, 2011 at 06:49:53PM +0200, Jens Axboe wrote:
>> I realize that, in fact it's already safe as long as you pass in 'true'
>> for __blk_run_queue(). Before I had rewritten it to move the running
>> out, so that makes the trick a little difficult. This afternoon I also
>> tested it and saw no noticable difference, but I'll probably just do it
>> anyway as it makes sense.
> 
> We still need the lock for __elv_add_request, so we'll need to keep the
> logic anyway.  But splitting out the just queue to kblockd case from
> __blk_run_queue and giving the latter a sane prototype still sounds
> like a good idea to me.
> 
> Btw, now that we don't call the request_fn directly any more and thus
> can't block, can the unplugging be moved into the preempt notifiers?

It was only partly the reason, there's still the notice on preempt
(instead of schedule) and the runqueue lock problem. And if we allow
preempt, then we need to do disable preempt around all the plug logic.

-- 
Jens Axboe

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