Serge E. Hallyn writes:
> While investigating the inordinate performance impact one of my patches
> seemed to be having, we tracked it down to two hlist_for_each_entry
> loops, and finally to the prefetch instruction in the loop.
I would be interested to know what results you get if you leave the
loops using hlist_for_each_entry but change prefetch() and prefetchw()
to do the dcbt or dcbtst instruction only if the address is non-zero,
like this:
static inline void prefetch(const void *x)
{
if (x)
__asm__ __volatile__ ("dcbt 0,%0" : : "r" (x));
}
static inline void prefetchw(const void *x)
{
if (x)
__asm__ __volatile__ ("dcbtst 0,%0" : : "r" (x));
}
It seems that doing a prefetch on a NULL pointer, while it doesn't
cause a fault, does waste time looking for a translation of the zero
address.
Paul.
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