From: Andy Lutomirski <email@example.com> To: Peter Zijlstra <firstname.lastname@example.org> Cc: David Ahern <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, LKML <email@example.com>, firstname.lastname@example.org Subject: Re: deadlock in scheduler enabling HRTICK feature Date: Thu, 27 Jun 2013 12:18:04 -0700 [thread overview] Message-ID: <51CC8FEC.email@example.com> (raw) In-Reply-To: <20130627105303.GD27378@dyad.programming.kicks-ass.net> On 06/27/2013 03:53 AM, Peter Zijlstra wrote: > 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. Supposedly, on really new x86 systems, the TSC deadline timer is so fast to reprogram that this isn't worth it. I wonder if the general timing code should have a way to indicate that a given clockevent is (a) very fast and (b) is actually locked to a clocksource as opposed to just having a vaguely accurately calibrated frequency. --Andy
next prev parent reply other threads:[~2013-06-27 19:18 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 2013-06-27 12:28 ` Mike Galbraith 2013-06-27 13:06 ` Ingo Molnar 2013-06-27 19:18 ` Andy Lutomirski [this message] 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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