Messages in this thread | | | Date | Mon, 13 Sep 2010 11:25:14 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr_running |
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* Steven Rostedt (rostedt@goodmis.org) wrote: > On Mon, 2010-09-13 at 16:16 +0200, Peter Zijlstra wrote: > > > > > - if (delta_exec < sysctl_sched_min_granularity) > > > > - return; > > > > > > Well, the reason why this test is here seems to be that we don't want to trigger > > > "resched_task" more often than needed, and here it's defined by the granularity. > > > > Right, but its wrong for the weighted case. Letting a light task run > > that long will make its latency suck. > > > > > I don't quite see with what you are replacing this, other than "let's set the > > > resched flag all the time to save a 32-bit division". I figure out it's more > > > expensive the call the scheduler than to do a 32-bit div. > > > > The more divs we put it, the more expensive it all becomes. > > > > What about: > > if (delta_exec < sysctl_sched_min_granularity || > delta_exec < __sched_gran(cfs_rq->nr_running)) > > This way we avoid the div when delta_exec is less than the > min_granularity, and then we can do the div to perhaps avoid a needless > resched?
Please note that my patch does not even take the 32-bit div when there are less than 4 threads running on the system.
So I'm not at all sure we're trying to optimize an important case here.
Mathieu
> > -- Steve > >
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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