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From: Thomas Gleixner <tglx@linutronix.de>
To: Jens Axboe <jaxboe@fusionio.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Ingo Molnar <mingo@elte.hu>, Tejun Heo <tj@kernel.org>
Subject: Re: [RFC][PATCH 1/3] sched, block: Move unplug
Date: Wed, 22 Jun 2011 16:30:38 +0200 (CEST)	[thread overview]
Message-ID: <alpine.LFD.2.02.1106221628560.11814@ionos> (raw)
In-Reply-To: <4E01F5D6.1020107@fusionio.com>

On Wed, 22 Jun 2011, Jens Axboe wrote:
> On 2011-06-22 15:53, Thomas Gleixner wrote:
> > On Wed, 22 Jun 2011, Jens Axboe wrote:
> > Is that a real problem or just a "we have no clue what might happen"
> > countermeasure? The plug list should not be magically refilled once
> > it's split off so this should not recurse endlessly, right? If it does
> > then we better fix it at the root cause of the problem and not by
> > adding some last resort band aid into the scheduler code.
> 
> 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.
 
> We are talking past each other again. Flushing on going to sleep is
> needed. Placement of that call was pretty much left in the hands of the
> scheduler people. I personally don't care where it's put, as long as it
> does what is needed.

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

	tglx

  reply	other threads:[~2011-06-22 14:30 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-06-21 23:34 [RFC][PATCH 0/3] Move WQ,unplug scheduler hooks Peter Zijlstra
2011-06-21 23:34 ` [RFC][PATCH 1/3] sched, block: Move unplug Peter Zijlstra
2011-06-22  7:01   ` Jens Axboe
2011-06-22 13:53     ` Thomas Gleixner
2011-06-22 14:01       ` Jens Axboe
2011-06-22 14:30         ` Thomas Gleixner [this message]
2011-06-22 14:38           ` Peter Zijlstra
2011-06-22 15:08             ` Vivek Goyal
2011-06-22 16:04               ` Jens Axboe
2011-06-21 23:34 ` [RFC][PATCH 2/3] sched, workqueue: Move WQ-sleeper wakeup Peter Zijlstra
2011-06-22  9:24   ` Tejun Heo
2011-06-22  9:27     ` Peter Zijlstra
2011-06-22  9:37       ` Tejun Heo
2011-06-22 13:47     ` Thomas Gleixner
2011-06-21 23:34 ` [RFC][PATCH 3/3] block: Break long IRQ disabled region Peter Zijlstra
2011-06-22  7:03   ` Jens Axboe

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