Hi, At 12:19 PM 11/2/2001 -0800, Stephan T. Lavavej wrote: >Will Prime95 be optimized to take advantage of >simultanous multithreading processors? Perhaps >some part of the FFT computation can be done >with multiple threads, so a SMT processor could >devote more power to one while the other is >waiting on memory or something.
A good theoretical question! The details on Intel's SMT implementation are not out yet, but the information we have now suggests that SMT could be a big winner for modern CPUs. SMT will be implemented in some versions of the P4 soon. SMT for those that don't know makes one P4 CPU look like 2 CPUs to the operating system. Each "virtual CPU" has its own set of registers and each runs a different program (actually a different "thread"). The real CPU can now execute instructions from either virtual CPU. Why is this good? Well, the P4 CPU is often stalled waiting for a instruction dependencies or memory accesses or whatever. With SMT the CPU now has more instructions to choose from in scheduling to keep the functional units busy. Better yet, it is guaranteed that there are no dependencies on instructions from different virtual CPUs. Intel states they are seeing up to 30% improvements in CPU throughput. Can prime95 take advantage of SMT? I'm skeptical. If the FFT is broken up to run in two threads, I'm afraid L2 cache pollution will negate any advantage of SMT. Of course, I'm just guessing - to test this theory out we should compare our throughput running 1 vs. 2 copies of prime95 on an SMT machine. -- George _________________________________________________________________________ Unsubscribe & list info -- http://www.scruz.net/~luke/signup.htm Mersenne Prime FAQ -- http://www.tasam.com/~lrwiman/FAQ-mers
