On 04-Nov-03, Ognen Duzlevski wrote: > Could someone educate me on the importance of turning off hyperthreading? > I guess I've been sleeping in the past several months... Current Linux kernels don't know how to schedule to it; they see four distinct CPUs. If you run two single threaded jobs on a machine with hyperthreading enabled, it's possible that that the scheduler will decide to put both on the same physical CPU, and leave the other one free. This will not happen if hyperthreading is disabled, and each job will get a physical CPU to itself. So, if you run multithreaded code exclusively, or predominantly, switch hypethreading on. If you principally run single threaded jobs, switch it off, until such time as you're running a kernel with a scheduler which understands hyperthreading (I believe there are some patches to do this, now) Tim -- Dr Tim Cutts Informatics Systems Group Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, UK