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From: Peter Zijlstra <peterz@infradead.org>
To: David Ahern <dsahern@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	tglx@linutronix.de
Subject: Re: deadlock in scheduler enabling HRTICK feature
Date: Thu, 27 Jun 2013 12:53:03 +0200	[thread overview]
Message-ID: <20130627105303.GD27378@dyad.programming.kicks-ass.net> (raw)
In-Reply-To: <20130627104309.GQ28407@twins.programming.kicks-ass.net>

On Thu, Jun 27, 2013 at 12:43:09PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 26, 2013 at 10:46:33AM -0600, David Ahern wrote:
> > On 6/26/13 1:05 AM, Peter Zijlstra wrote:
> > >>What is the expectation that the feature provides? not a whole lot of
> > >>documentation on it. I walked down the path wondering if it solved an odd
> > >>problem we are seeing with the CFS in 2.6.27 kernel.
> > >
> > >Its supposed to use hrtimers for slice expiry instead of the regular tick.
> > 
> > So theoretically CPU bound tasks would get preempted sooner? That was my
> > guess/hope anyways.
> 
> Doth the below worketh?
> 

Related to all this; the reason its not enabled by default is that mucking
about with hrtimers all the while is god awful expensive.

I've had ideas about making this a special purpose 'hard-coded' timer in the
hrtimer guts that's only ever re-programmed when the new value is sooner.

By making it a 'special' timer we can avoid the whole rb-tree song and dance;
and by taking 'spurious' short interrupts we can avoid prodding the hardware
too often.

Then again; Thomas will likely throw frozen seafood my way for even proposing
stuff like this and I'm not even sure that's going to be enough to make the
cost acceptable.

  reply	other threads:[~2013-06-27 10:53 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-06-25 21:05 David Ahern
2013-06-25 21:17 ` Peter Zijlstra
2013-06-25 21:20   ` David Ahern
2013-06-26  7:05     ` Peter Zijlstra
2013-06-26 16:46       ` David Ahern
2013-06-27 10:43         ` Peter Zijlstra
2013-06-27 10:53           ` Peter Zijlstra [this message]
2013-06-27 12:28             ` Mike Galbraith
2013-06-27 13:06             ` Ingo Molnar
2013-06-27 19:18             ` Andy Lutomirski
2013-06-27 20:37               ` Peter Zijlstra
2013-06-27 22:28           ` David Ahern
2013-06-28  9:00             ` Ingo Molnar
2013-06-28  9:18               ` Peter Zijlstra
2013-07-12 13:29                 ` [tip:sched/core] sched: Fix HRTICK tip-bot for Peter Zijlstra
2013-06-28  9:09             ` deadlock in scheduler enabling HRTICK feature Peter Zijlstra
2013-06-28 17:28               ` David Ahern

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