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Date: Fri, 17 Nov 2006 20:31:33 -0800 (PST) From: dean gaudet <dean@...tic.org> To: Bela Lubkin <blubkin@...are.com> cc: Andi Kleen <ak@...e.de>, linux-kernel@...r.kernel.org, mingo@...e.hu Subject: RE: touch_cache() only touches two thirds On Fri, 17 Nov 2006, dean gaudet wrote: > another pointer chase arranged to fill the L1 (or L2) using many many > pages. i.e. suppose i wanted to traverse 32KiB L1 with 64B cache lines > then i'd allocate 512 pages and put one line on each page (pages ordered > randomly), but colour them so they fill the L1. this conveniently happens > to fit in a 2MiB huge page on x86, so you could even ameliorate the TLB > pressure from the microbenchmark. btw, for L2-sized measurements you don't need to be so clever... you can get away with a random traversal of the L2 on 128B boundaries. (need to avoid the "next-line prefetch" issues on p-m/core/core2, p4 model 3 and later.) there's just so many more pages required to map the L2 than any reasonable prefetcher is going to have any time soon. -dean > the benchmark i was considering would be like so: > > switch to cpu m > scrub the cache > switch to cpu n > scrub the cache > traverse the coloured list and modify each cache line as we go > switch to cpu m > start timing > traverse the coloured list without modification > stop timing - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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