Re: dcache_rcu [performance results]

[Andrew Morton <akpm@digeo.com>]

Dipankar Sarma wrote:
> 
> [ dcache-rcu ]
> 
> Anton (Blanchard) did some benchmarking with this
> in a 24-way ppc64 box and the results showed why we need this patch.
> Here are some performace comparisons based on a multi-user benchmark
> that Anton ran with vanilla 2.5.40 and 2.5.40-mm.
> 
> http://lse.sourceforge.net/locking/dcache/summary.png
> 
> base = 2.5.40
> base-nops = 2.5.40 but ps command in benchmark scripts commented out
> mm = 2.5.40-mm
> mm-nops = 2.5.40-mm but ps command in benchmark scripts commented out
> 

I'm going to need some help understanding what's going on in
there.  I assume the test is SDET (there, I said it), which
simulates lots of developers doing developer things on a multiuser
machine.  Lots of compiling, groffing, etc.

Why does the removal of `ps' from the test script make such a huge
difference?  That's silly, and we should fix it.

And it appears that dcache-rcu made a ~10% difference on a 24-way PPC64,
yes?  That is nice, and perhaps we should take that, but it is not a
tremendous speedup.

Thanks.