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

From: NeilBrown
Date: Tue Apr 12 2011 - 17:08:46 EST

On Wed, 13 Apr 2011 00:34:52 +1000 Dave Chinner <david@xxxxxxxxxxxxx> wrote:

> On Tue, Apr 12, 2011 at 03:45:52PM +0200, Jens Axboe wrote:
> Not until you
> > schedule() or call blk_finish_plug(), both of which are events that you
> > can control.
> Well, not really - now taking any sleeping lock or waiting on
> anything can trigger a plug flush where previously you had to
> explicitly issue them. I'm not saying what we had is better, just
> that there are implicit flushes with your changes that are
> inherently uncontrollable...

It's not just sleeping locks - if preempt is enabled a schedule can happen at
any time - at any depth. I've seen a spin_unlock do it.

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