Robin Humble ha scritto:
> On Tue, Oct 12, 2004 at 10:58:48AM +0800, L WK wrote:
>
>>I have bought a Dell with a P4 2.8G hyperthread CPU. I wonder if it's
>>possible to make use of the hyperthread in my parallel program.
>
> However if you have SMP (>1 cpu) and hyperthreading then you need the
> kernel's cpu scheduler to be VERY hyperthreading aware, otherwise you
> can get code _slowdowns_. Does anyone know if linux 2.6 kernels are
> smart enough not to screw up yet?
According to some linux kernel mailing lists, kernel version >= 2.4.26
and any 2.6 should be HT aware; and actually I can say that, on 2.4.27,
enabling HT (from bios) does not improve neither slow down my typical
LAM-MPI application and, strange to say, the performance is almost
exactly the same when using either 2 or 4 of the logical processors per
node (I expected only worsening with 4 processes, so I do not consider
it a bad result). Note that with kernel 2.4.22 (and I guess up to
2.4.25) it was almost necessary to disable HT for parallel applications
otherwise performance was worse and unstable even using just as many MPI
processes as the number of physical processors.
best regards, Davide
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