some RCU dcache and ratcache results

[Anton Blanchard]

> > Not for this, I did do some benchmarking of the RCU dcache patches a
> > while ago which I should post.
> 
> Please do ;-) This shows why we need to ease the pressure on dcache_lock.

OK :) Here is a graph I made a while ago. It is on a 32 way ppc64 box
running dbench.

http://samba.org/~anton/linux/dcache/summary.png

rat - radix-tree pagecache patch
dcache - RCU dcache patch
ext2 - rusty's BKL removal from ext2 patch

Not surprisingly the RCU dcache patch gave a large improvement in
dbench. While dbench may not be the greatest of benchmarks I am also
seeing a lot of dcache_lock contention on large zero copy workloads (eg 8
way specweb).

> > I didnt get a chance to run lockmeter, I tend to use the kernel profiler
> > and use a hacked readprofile (originally from tridge) that displays
> > profile hits vs assembly instruction. Thats usually good enough to work
> > out which spinlocks are a problem.
> 
> Is this a PPC only hack ? Also, where can I get it ?

I thought tridge put it into cvs somewhere, I'll find out the details
from him.

Anton