Re: A scrub daemon (prezeroing)

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

On Thu, 2005-02-03 at 22:26 -0800, Christoph Lameter wrote:
> On Fri, 4 Feb 2005, Paul Mackerras wrote:
> 
> > As has my scepticism about pre-zeroing actually providing any benefit
> > on ppc64.  Nevertheless, the only definitive answer is to actually
> > measure the performance both ways.
> 
> Of course. The optimization depends on the type of load. If you use a
> benchmark that writes to all pages in a page then you will see no benefit
> at all. For a kernel compile you will see a slight benefit. For processing
> of a sparse matrix (page tables are one example) a significant benefit can
> be obtained.

If you have got to the stage of doing "real world" tests, I'd be
interested to see results of tests that best highlight the improvements.

I imagine many general purpose server things wouldn't be helped much,
because they'll typically have little free memory, and will be
continually working and turning things over.

A kernel compile on a newly booted system? Well that is a valid test.
It is great that performance doesn't *decrease* in that case :P

Of course HPC things may be a different story. It would be good to
see your gross improvement on typical types of workloads that can best
leverage this - and not just initial ramp up phases while memory is
being faulted in, but the the full run time.

Thanks,
Nick



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