Re: [RFC patch 1/2] sched: dynamically adapt granularity with nr_running

Steven Rostedt
2010-09-13T15:39:32Z

On Mon, 2010-09-13 at 11:25 -0400, Mathieu Desnoyers wrote:

> > > 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.

If we have 5 threads running and hit this where delta_exec is <
sched_min_granularity, then we do have that div, right? Question is, how
often do we hit this condition where delta_exec is less while running
more that 4 threads?

-- Steve