Emil Briggs writes:
> >
> >> The huge increase probably comes from the facts that
> >> x11amp is switching CPU too often and the more
> >> primitive L2 cache mapping on Neptune boards.
> >
> >Well CPU switching doesn't explain my observations as I have lots of
> >instances of seeing it on UP machines.
> >
> >Dunno about the cache issues - to be honest I don't know why different
> >page layouts in physical RAM makes such a big difference...
> >
> Maybe TLB misses?
That's what I thought, but it was pointed out to me that TLB refils
for x86 are done in hardware and are pretty fast. Upon investigation
it turned out to be L2 cache misses due to cache line aliasing.
Note that the cache will cache physical memory, hence the layout of
physical pages matters much.
The solution: page colouring (thanks to DaveM for his tips). I tried
that and it works. The patch is crude and can slow down process
startup times, and it requires a system with plenty of RAM to spare,
but it does work. If people want to try this, I could be encouraged to
post a patch.
Regards,
Richard....
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