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

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Date:	Thu, 9 Nov 2006 22:18:13 -0800
From:	"Chen, Kenneth W" <kenneth.w.chen@...el.com>
To:	"'Christoph Lameter'" <clameter@....com>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"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 Tuesday, November 07, 2006 1:50 PM
> On Tue, 7 Nov 2006, Chen, Kenneth W wrote:
> > > What broke the system was the disabling of interrupts over long time 
> > > periods during load balancing.
> > The previous global load balancing tasket could be an interesting data point.
> 
> Yup seems also very interesting to me. We could drop the staggering code 
> f.e. if we would leave the patch as is. Maybe there are other ways to 
> optimize the code because we know that there are no concurrent 
> balance_tick() functions running.
> 
> > Do you see a lot of imbalance in the system with the global tasket?  Does it
> > take prolonged interval to reach balanced system from imbalance?
> 
> I am rather surprised that I did not see any problems but I think we would 
> need some more testing. It seems that having only one load balance 
> running at one time speeds up load balacing in general since there is 
> less lock contention.


I ran majority of micro-benchmarks from LKP project with global load
balance tasklet. (http://kernel-perf.sourceforge.net)

Result is here:
http://kernel-perf.sourceforge.net/sched/global-load-bal.txt

All results are within noise range.  The global tasklet does a fairly good job especially on context switch intensive workload like
aim7, volanomark, tbench
etc.  Note all machines are non-numa platform.

Base on the data, I think we should make the load balance tasklet one per numa
node instead of one per CPU.

- Ken
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