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dtripp 2013-02-19 19:07

AMD vs Intel
I'm running p95v279 on two types of nodes, a dual 6 core opteron and a 4 core Xeon. The Xeons are wiping the floor with the Opterons even though the Opteron has 3 times as many cores and 96 Gigs of RAM compared to 16 for the Xeons. I'm guessing the pre-compiles binaries strongly favor Intel.

Has anyone tried compiling from source for AMD and seen better performance?

sdbardwick 2013-02-19 20:09

For Prime95 LL tests, Intel silicon really is that much better than AMD.

Rough performance comparison based on my observations:
4 bulldozer cores (Opteron 4280) @ 2.8 GHz =
2 K10 cores (Opteron 6128) @ 2.0 GHz <
1 i5-2500 core @ 3.4 GHz.

Intel's implementation of SIMD (AVX) along with better cache performance (and I believe better memory controllers) really kills AMD for Prime95.

Dubslow 2013-02-19 20:15

Recompiling with different compiler options won't help: all the speed critical parts are written directly in assembly anyways, and despite George Woltman's best efforts, the AMD parts just aren't that fast.

Memory size doesn't play a role in speed (around 7-8MB required per test), and memory speed only plays a role insofar as nothing is bottlenecked.

ewmayer 2013-02-19 20:20

See [url=]here[/url] for details on how AMD screwed the pooch when it comes to SIMD (SSE2 badly, AVX catastrophically).

There may be some gains to be realized from use of fused mul/add (in SSE2 mode only, though - AMD AVX is literally worse than useless here) on the more recent chips, but from the perspective of someone like George who needs to choose his coding time carefully, that's a lot of work just to get a poor chip design to "suck less".

Intel's forthcoming implementation of AVX2 will only make the performance disparity that much greater.

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