Messages in this thread | | | Subject | Re: deadlock in scheduler enabling HRTICK feature | From | Mike Galbraith <> | Date | Thu, 27 Jun 2013 14:28:01 +0200 |
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On Thu, 2013-06-27 at 12:53 +0200, 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.
That cost sprang to mind when you mentioned that deadline needs hrtick.
> 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.
Could be worse, flaming marshmallows stick.
-Mike
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