20031016, 13:07  #1 
Mar 2003
Braunschweig, Germany
E2_{16} Posts 
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 LLinstance and one TFinstance. Actually, between 2^64 and 2^65 i get a netthroughput 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 hardwaresection later... Tau 
20031016, 15:30  #2 
Mar 2003
Braunschweig, Germany
2×113 Posts 
... 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 
20031016, 22:05  #3 
P90 years forever!
Aug 2002
Yeehaw, FL
2×4,079 Posts 
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.

20031017, 06:30  #4 
Mar 2003
Braunschweig, Germany
2×113 Posts 
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 HTmachine alone participates in GIMPS, would it not improve overall GIMPS throughput if HTUsers could choose in the client to use a different table for the TFlimits 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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