On Saturday 21 September 2002 21:20, Daran wrote: > Could this feature of forthcoming Intel processors be used to do trial > factorisation without adversely impacting upon a simultaneous LL? Could > this be easily implemented?
1) _Existing_ Pentium 4 Xeons have hyperthreading capability. 2) Implementation is easy; just run two processes - one LL & one TF - assigning one to each virtual processor. In fact there's no other way to implement: you can't have one process running in multiple virtual processors simultaneously with hyperthreading technology alone. 3) I reckon there would be a very significant performance hit. Temporary registers, instruction decoders etc. are shared so any pressure whatsoever on the "critical path" would cause a performance drop - even if the code in the two processes could be guaranteed to stay phase locked so that there was no simultaneous call on a particular execution unit. (In practise I think unregulated phase drifts would result in a phase locked clash, since this appears to be the most stable state). You would probably get 20-30% more _total_ throughput this way than you would be running LL & DC assignments in series, i.e. the LL test speed would be at best 2/3 of what it would be without TF running in parallel on the same CPU. One benefit of hyperthreading technology for compute-bound processes in an interactive environment - provided you're running only one compute-bound process per _physical_ processor - is that the extra capacity helps the system to react more quickly to interactive loads, so it's a lot less likely that foreground users will notice the background CPU load. Regards Brian Beesley _________________________________________________________________________ Unsubscribe & list info -- http://www.ndatech.com/mersenne/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
