Messages in this thread | | | Date | Mon, 28 Oct 2013 17:20:45 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] x86: Run checksumming in parallel accross multiple alu's |
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* Neil Horman <nhorman@tuxdriver.com> wrote:
> Base: > 0.093269042 seconds time elapsed ( +- 2.24% ) > Prefetch (5x64): > 0.079440009 seconds time elapsed ( +- 2.29% ) > Parallel ALU: > 0.087666677 seconds time elapsed ( +- 4.01% ) > Prefetch + Parallel ALU: > 0.080758702 seconds time elapsed ( +- 2.34% ) > > So we can see here that we get about a 1% speedup between the base > and the both (Prefetch + Parallel ALU) case, with prefetch > accounting for most of that speedup.
Hm, there's still something strange about these results. So the range of the results is 790-930 nsecs. The noise of the measurements is 2%-4%, i.e. 20-40 nsecs.
The prefetch-only result itself is the fastest of all - statistically equivalent to the prefetch+parallel-ALU result, within the noise range.
So if prefetch is enabled, turning on parallel-ALU has no measurable effect - which is counter-intuitive. Do you have an theory/explanation for that?
Thanks,
Ingo
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