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SubjectRe: Fw: potential /dev/urandom scalability improvement
FromAndi Kleen <>
DateSat, 27 Mar 2004 02:29:12 +0100
Andrew Morton <akpm@osdl.org> writes:
>
> I think this gets it right, but I probably screwed something up.
>
> static inline void prefetch_range(void *addr, size_t len)
> {
> #ifdef ARCH_HAS_PREFETCH
> 	char *cp;
> 	unsigned long end;
>
> 	end = ((unsigned long)addr + len + PREFETCH_STRIDE - 1);
> 	end &= ~(PREFETCH_STRIDE - 1);
>
> 	for (cp = addr; cp < (char *)end; cp += PREFETCH_STRIDE)
> 		prefetch(cp);
> #endif
> }

The memory/bus controller usually only has a limited queue of
outstanding transactions and for a big buffer you will likely overflow
it. Also usually on modern CPUs it is enough to do prefetch for 2-3
cache lines at the beginning, then an automatic hardware prefetcher
will kick in and take care of the rest.

-Andi

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