Messages in this thread | | | Date | Fri, 4 Feb 2005 10:39:10 +1100 | From | Paul Mackerras <> | Subject | Re: A scrub daemon (prezeroing) |
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Rik van Riel writes:
> I'm not convinced. Zeroing a page takes 2000-4000 CPU > cycles, while faulting the page from RAM into cache takes > 200-400 CPU cycles per cache line, or 6000-12000 CPU > cycles.
On my G5 it takes ~200 cycles to zero a whole page. In other words it takes about the same time to zero a page as to bring in a single cache line from memory. (PPC has an instruction to establish a whole cache line of zeroes in modified state without reading anything from memory.)
Thus I can't see how prezeroing can ever be a win on ppc64.
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