Hi,
In Linux, one can apparently set processor affinity (or, in this case
core affinity) with 'taskset'. The command is used like this:
taskset <bitmask> command
where <bitmask> is a hexadecimal bit mask with the cpus to use (in a
format like 0xff, where 0xff enables the first 8 cpus on a system).
For mdrun using MPI on a core i7, with 4 (or fewer) tasks each on
their own real core it would be
mpirun -np 4 taskset 0x55 mdrun
I don't have access to a cpu with hyperthreading right now so I can't
check whether it actually works, though.
Sander
On Sep 15, 2009, at 18:41 , Berk Hess wrote:
That is incorrect.
A Core I7 is about 40% faster with hyperthreading turned off.
A Core I7 is about 65% faster with hyperthreading turned on
and running 8 processes.
What you should NOT do (but which can happen very easily)
is running on a Core I7 with hyperthreading turned on and using
only 4 processes. In that case the processes are distributed
randomly over the 8 virtual and 4 real cores and the chance
is very high that at least one real cores gets 2 mdrun processes
and your simulation is nearly 50% slower than it could be.
If somebody has a solution for this problem under Linux,
that would be extremely useful.
Berk
> Date: Tue, 15 Sep 2009 14:20:09 +0200
> From: [email protected]
> To: [email protected]
> Subject: Re: [gmx-users] Core i7 vs Core2Quad
>
> I7 about 20% faster at same clock speed ...
> Antoine
>
>
>
> marcos a écrit :
> > Hi,
> >
> > I wander if somebody has compared Core i7 vs Core2Quad in Gromacs
> > simulations.
> > Is Core i7 faster in a per clock basis?
> >
> > Marcos.
> >
> >
> > Marcos Villarreal
> >
> >
> > _______________________________________________
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What can you do with the new Windows Live? Find out
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