On 03.22, Dan Maas wrote: > Is there a canonical way for user-space software to determine how many > real CPUs are present in a system (as opposed to HyperThreaded or > otherwise virtual CPUs)? >
This is 2xXeonHT, is, 4 cpus on 2 packages: cat /proc/cpuinfo: processor : 0 ... physical id : 0 siblings : 2 core id : 0 cpu cores : 1 processor : 1 ... physical id : 0 siblings : 2 core id : 0 cpu cores : 1 processor : 2 ... physical id : 3 siblings : 2 core id : 3 cpu cores : 1 processor : 3 ... physical id : 3 siblings : 2 core id : 3 cpu cores : 1 So something like: cat /proc/cpuinfo | grep 'core id' | uniq | wc -l would give you the number of packages or 'real cpus'. Then you have to choose which ones are unrelated. Usually evens are siblings of odds, but I won't trust on it... > We have an application that for performance reasons wants to run one > process per CPU. However, on a HyperThreaded system /proc/cpuinfo > lists two CPUs, and running two processes in this case is the wrong > thing to do. (Hyperthreading ends up degrading our performance, > perhaps due to cache or bus contention). > I always hear people about HT 'degrading' performance. Obviously you don't get a 200%, but it is always better than 100%. With my simulation code, in which I did not anything special for HT (it uses my 4 cpus as 'real' ones), I usually get a 125-130% gain. So the theoretical performance loos true. Your application behaviour has to be really nasty to run slower with 2 threads on an HT-P4 that with one thread. Hope this helps. -- J.A. Magallon <jamagallon()able!es> \ Software is like sex: werewolf!able!es \ It's better when it's free Mandrakelinux release 10.2 (Cooker) for i586 Linux 2.6.11-jam6 (gcc 3.4.3 (Mandrakelinux 10.2 3.4.3-6mdk)) #1 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
