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On 26 Jan 2002, Andi Kleen wrote: > > It doesn't explain the Athlon speedups. On athlon cli is ~4 cycles. .. and it probably serializes the instruction stream. Look at the patch. The _only_ thing it does for the system call path is: - remove the "cli" - change cmpl $0,.. jne cmp $0,.. jne into movl ..,reg testl reg,reg jne and the latter may be worth a cycle (or two, if the CPU happens to like the second form better for some other reason), but it's certainly not noticeable. A 3.4% improvement is equivalent to something like 9 cycles, so the "cli" being faster on Athlon than on a PIII certainly explains why it's less noticeable on the Athlon, but it still makes me suspect that the _real_ cost of the cli is on the order of 8 cycles. It should be eminently testable. Just remove the cli from the standard kernel, and do before-and-after tests. Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.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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