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Old 2003-10-16, 13:07   #1
TauCeti
 
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Default Is TF from 2^64 to 2^65 using SSE2?

I know that whatsnew.txt states for Version 22.7 : "Trial factoring above 2^64 on a P4 now uses the SSE2 instructions."

I just want to confirm here, that this is really the case, because i get some strange results using Hyperthreading simultanously with one LL-instance and one TF-instance.
Actually, between 2^64 and 2^65 i get a net-throughput increase of roughly 44% using HT compared to 20% between 2^63 and 2^64.

Before i started to test HT, i expected a performance _decrease_, once TF and LL both start using SSE2.

If 2^65 on P4 is really SSE2, then more on this topic from me in another thread in the hardware-section later...

Tau
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Old 2003-10-16, 15:30   #2
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... hmmm, my strange results are still there but now i have tested a 2^67 TF with the same result and i am pretty sure SSE2 is used there. More in the hardware section...

Tau
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Old 2003-10-16, 22:05   #3
Prime95
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The FFT is using floating point SSE2 instructions. Trial factoring is using the integer SSE2 instructions. It makes sense that HT would benefit in this scenario.
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Old 2003-10-17, 06:30   #4
TauCeti
 
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Thanks for the explanation. Maybe i really shold try to understand SSE2 in detail

So - assuming for the sake of the argument - that only one HT-machine alone participates in GIMPS, would it not improve overall GIMPS throughput if HT-Users could choose in the client to use a different table for the TF-limits because in:

factoring_cost < chance_of_finding_factor * 2 * primality_test_cost

the factoring cost is reduced by about 40% using HT?

Tau
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