Re: OT? hypertread on or off for SMP kernel
In article <[🔎] 1102603975.27189.503.camel@localhost.localdomain>,
michael <linux@networkingnewsletter.org.uk> 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.
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