On Thu, 2004-12-09 at 16:53, Miquel van Smoorenburg wrote: > In article <[EMAIL PROTECTED]>, > michael <[EMAIL PROTECTED]> wrote: > >However, for one simple test (v.low memory, v.low comms, high compute) > >case which is Fortran90 compiled using mpich, I actually found turning > >HT off helped -- when it was on then for -np 2 there was no speed up > >(top implied they ran on same physical processor). I presume this was > >because the CPU was fully busy anyhow so the 2nd thread had to wait (you > >seem to imply the opposite but I don't follow why!). > > Turning on the "SMT scheduler support" in the kernel is supposed > to prevent exactly this. If two jobs are runnable, they will be > run on 2 different CPUs (if you have them), not on 1 CPU with 2 threads. > > Mike. >
Thanks that's useful. The question thus becomes whether I can compile 'mpich' such that it can take advantage of SMT and how well it can, or not. Michael -- To UNSUBSCRIBE, email to [EMAIL PROTECTED] with a subject of "unsubscribe". Trouble? Contact [EMAIL PROTECTED]
