On the effect of branch mispredictions in the Squeak VM
John M McIntosh
johnmci at mac.com
Mon Jul 7 09:36:24 UTC 2003
> From: "Andreas Raab" <andreas.raab at g...>
> ...
> I set up a little benchmark (which is attached) that runs the same
> bytecodes
> with some re-ordering (applied to maximize/minimize the effect of the
> dispatch) and run it. Here are the results:
>
> iterations well-predicted(msecs) mispredicted(msecs)
> 10 0 0
> 100 0 0
> 1000 0 1
> 10000 3 7
> 100000 24 68
> 1000000 247 673
> 10000000 2463 6722
>
> The interesting fact of the matter is that we spend about 2.7 times as
> much
> when we have branch mispredictions as without them. I'd be delighted if
> someone could review the benchmarks itself in order to ensure that I
> haven't
> done anything wrongly and that the results itself are valid.
>
My numbers using mac vm 3.5.2b1 (500Mhz G3) are:
10 0 0
100 0 0
1000 1 1
10000 8 7
100000 77 78
1000000 797 781
10000000 7817 7861
again
10 0 0
100 0 0
1000 1 1
10000 15 8
100000 78 77
1000000 786 776
10000000 7809 7819
Perhaps someone else can confirm these?
--
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John M. McIntosh <johnmci at smalltalkconsulting.com> 1-800-477-2659
Corporate Smalltalk Consulting Ltd. http://www.smalltalkconsulting.com
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