Re: spec2k comparison of gcc 4.1 and 4.2 on AMD K8

["Richard Guenther" <richard dot guenther at gmail dot com>]

On 2/27/07, Menezes, Evandro <evandro.menezes@amd.com> wrote:
> Honza,
>
> > Well, rather than unstable, they seems to be more memory layout
> > sensitive I would say. (the differences are more or less reproducible,
> > not completely random, but independent on the binary itself. I can't
> > think of much else than memory layout to cause it).  I always wondered
> > if things like page coloring have chance to reduce this noise, but I
> > never actually got around trying it.
>
> You didn't mention the processors in your systems, but I wonder if they are dual-core.  If so, perhaps it's got to do with the fact that each K8 core has its own L2, whereas C2 chips have a shared L2.  Then, try preceding "runspec" with "taskset 0x02" to avoid the process from hopping between cores and finding cold caches (though the kernel strives to stick a process to a single core, it's not perfect).

Well, both britten and haydn are single core, two processor systems.  For
SPEC2k6 runs the problem is that the 2gb ram of the machine are
distributed over both numa nodes, so with the memory requirements of
SPEC2k6 we always get inter-node memory traffic.  Vangelis is a single
processor, single core system (and the most stable one).  Any idea on
how to force to use local memory only for a process?

Richard.