linux-kernel - RE: + sched-use-tasklet-to-call-balancing.patch added to -mm tree

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Date:	Fri, 10 Nov 2006 18:05:28 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Christoph Lameter'" <clameter@....com>,
	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>, <akpm@...l.org>,
	<mm-commits@...r.kernel.org>, <nickpiggin@...oo.com.au>,
	<linux-kernel@...r.kernel.org>
Subject: RE: + sched-use-tasklet-to-call-balancing.patch added to -mm tree

Christoph Lameter wrote on Friday, November 10, 2006 5:01 PM
> On Fri, 10 Nov 2006, Ingo Molnar wrote:
> 
> > ok, that's what i suspected - what made the difference wasnt the fact 
> > that it was moved out of irqs-off section, but that it was running 
> > globally, instead of in parallel on every cpu. I have no conceptual 
> > problem with single-threading the more invasive load-balancing bits. 
> > (since it has to touch every runqueue anyway there's probably little 
> > parallelism possible) But it's a scary change nevertheless, it 
> > materially affects every SMP system's balancing characteristics.
> 
> We saw multiple issues. The first we saw was interrupt holdoff related 
> since IPIs took a long time to complete. The other was that multiple 
> load balance actions in multiple CPUs seem to serialize on the locks 
> trying each to move tasks off the same busy processor. So both better be 
> addressed.

So designate only one CPU within a domain to do load balance between groups
for that specific sched domain should in theory fix the 2nd problem you
identified.  Did you get a chance to look at the patch Suresh posted?

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