Re: -mm seems significanty slower than mainline on kernbench

[Nick Piggin <nickpiggin@yahoo.com.au>]

Peter Williams wrote:
> Nick Piggin wrote:

> I figured using the weights (which go away for nice=0 tasks) would make 
> it behave nicely with the rest of the load balancing code.

OK, if you keep working on it that would be great.

> > but I didn't quite look close enough to
> > work out what's going wrong.
>
>
> My testing (albeit on an old 2 cpu Celeron) showed no statistically 
> significant difference between with the patch and without.  If you 
> ignored the standard deviations and statistical practice and just looked 
> at the raw numbers you'd think it was better with the patch than without 
> it.  :-)
>
> I assume that Andy Whitcroft is doing a kernbench with the patch removed 
> from 2.6.15-mm3 (otherwise why would he ask for a patch to do that) and 
> I'm waiting to see how that compares with the run he did with it in. 
> There were other scheduling changes in 2.6.15-mm3 so I think this 
> comparison is needed in order to be sure that any degradation is still 
> due to my patch.
>
> Peter
> PS As load balancing maintainer, is the value 128 set in cement for 
> SCHED_LOAD_SCALE?  The reason I ask is that if it was changed to be a 
> multiple of NICE_TO_BIAS_PRIO(0) (i.e. 20) my modification could be made 
> slightly more efficient.

Not set in stone but it should really be a power of two because there are
quite a lot of multiplies and divides done with it.

--
SUSE Labs, Novell Inc.

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