Re: load balancing regression since commit 367456c7

From: Tim Chen
Date: Tue Apr 17 2012 - 12:44:46 EST

On Tue, 2012-04-17 at 14:09 +0200, Peter Zijlstra wrote:
> On Tue, 2012-04-10 at 18:06 -0700, Tim Chen wrote:
> > |--56.52%-- load_balance
> > | idle_balance
> > | __schedule
> > | schedule
> Ahh, I know why I didn't see it, I have a CONFIG_PREEMPT kernel and
> idle_balancing stops once its gotten a single task over instead of
> achieving proper balance.
> And since hackbench generates insanely long runqueues and the patch that
> caused your regression 'fixed' the lock-breaking it will now iterate the
> entire runqueue if needed to achieve balance, which hurts.
> I think the patch I send ought to work, let me try disabling
> --

yes, CONFIG_PREEMPT is turned off on my side. With the patch that you
sent, the slowed down went from a factor of 4 down to a factor 2.

So the run time is now twice as long vs four time as long vs v3.3


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