Re: [RFC PATCH v3 0/3] sched: simplify the select_task_rq_fair()

From: Ingo Molnar
Date: Fri Feb 22 2013 - 04:54:32 EST

* Mike Galbraith <efault@xxxxxx> wrote:

> On Fri, 2013-02-22 at 09:36 +0100, Peter Zijlstra wrote:
> > On Fri, 2013-02-22 at 10:37 +0800, Michael Wang wrote:
> > > But that's really some benefit hardly to be estimate, especially when
> > > the workload is heavy, the cost of wake_affine() is very high to
> > > calculated se one by one, is that worth for some benefit we could not
> > > promise?
> >
> > Look at something like pipe-test.. wake_affine() used to
> > ensure both client/server ran on the same cpu, but then I
> > think we added select_idle_sibling() and wrecked it again :/
> Yeah, that's the absolute worst case for
> select_idle_sibling(), 100% synchronous, absolutely nothing to
> be gained by cross cpu scheduling. Fortunately, most tasks do
> more than that, but nonetheless, select_idle_sibling()
> definitely is a two faced little b*tch. I'd like to see the
> evil b*tch die, but something needs to replace it's pretty
> face. One thing that you can do is simply don't call it when
> the context switch rate is incredible.. its job is to recover
> overlap, if you're scheduling near your max, there's no win
> worth the cost.

Couldn't we make the cutoff dependent on sched_migration_cost?
If the wakeup comes in faster than that then don't spread.


To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at