On Fri, 4 Feb 2005, Paul Mackerras wrote: > 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.
You need to think about this in a different way. Prezeroing only makes sense if it can avoid using cache lines that the zeroing in the hot paths would have to use since it touches all cachelines on the page (the ppc instruction is certainly nice and avoids a cacheline read but it still uses a cacheline!). The zeroing in itself (within the cpu caches) is extraordinarily fast and the zeroing of large portions of memory is so too. That is why the impact of scrubd is negligible since its extremely fast. The point is to save activating cachelines not the time zeroing in itself takes. This only works if only parts of the page are needed immediately after the page fault. All of that has been documented in earlier posts on the subject. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
