linux-kernel - Re: [RFC][PATCH 1/3] sched, block: Move unplug

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Date:	Wed, 22 Jun 2011 16:38:01 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Jens Axboe <jaxboe@...ionio.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>, Tejun Heo <tj@...nel.org>
Subject: Re: [RFC][PATCH 1/3] sched, block: Move unplug

On Wed, 2011-06-22 at 16:30 +0200, Thomas Gleixner wrote:
> > It is supposedly a real problem, not just an inkling. It's not about
> > recursing indefinitely, the plug is fairly bounded. But the IO dispatch
> > path can be pretty deep, and if you hit that deep inside the reclaim or
> > file system write path, then you get dangerously close. Dave Chinner
> > posted some numbers in the 2.6.39-rc1 time frame showing how close we
> > got.
> 
> Fair enough.

> Ok. So we move it out and keep the from_scheduler flag so that code
> does not go down the IO path from there. 

Won't punting the plug to a worker thread wreck all kinds of io
accounting due to the wrong task doing the actual io submission?
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