Re: [dm-devel] [PATCH 05/10] block: remove per-queue plugging

["hch infradead org" <hch infradead org>]

On Tue, Apr 12, 2011 at 02:58:46PM +0200, Jens Axboe wrote:
> Supposedly it's faster to do it inline rather than punt the dispatch.
> But that may actually not be true, if you have multiple plugs going (and
> thus multiple contenders for the queue lock on dispatch). So lets play
> it safe and punt to kblockd, we can always revisit this later.

Note that this can be optimized further by adding a new helper that just
queues up work on kblockd without taking the queue lock, e.g. adding a
new

void blk_run_queue_async(struct request_queue *q)
{
	if (likely(!blk_queue_stopped(q)))
		queue_delayed_work(kblockd_workqueue, &q->delay_work, 0);
}

And replacing all

	__blk_run_queue(q, true);

callers with that, at which point they won't need the queuelock any
more.