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

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Message-ID: <20110412165455.GB23764@infradead.org>
Date:	Tue, 12 Apr 2011 12:54:55 -0400
From:	"hch@...radead.org" <hch@...radead.org>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	"hch@...radead.org" <hch@...radead.org>,
	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 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?
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