On Tue, Oct 26, 1999 at 08:38:43AM -0400, Jasjeet Bagla wrote:
>
> Hi,
>
> I have an SMP box (PII 333MHz) with SuSE 6.1 running 2.2.13. I am using
> it to run large simulations. If i run one job, one cycle takes about 73
> minutes of CPU time. It i run two identical jobs, this goes up to a
> little more than 90 minutes. Both the jobs are big - they require 160MB
> of RAM each. I have 384MB so that should not be a problem, in principle.
> I suspect this is a scheduler problem. I want to know if something can
> be done about it.
>
Since your jobs use a lot of memory, I suspect that they also use
the memory a lot. That is, they perform operations on a multi-megabyte
dataset repeatedly, so that the data set each CPU works on doesn't
fit well in L1/L2 cache and actual main memory access is required.
If that holds, I guess what you're seeing is memory contention.
Memory access has been improved greatly on newer boards, but on my
dual PPro box at home, I can get ~100% speedup when the problems fit
in cache, and roughly 10-20% speedup on memory intensive problems.
You still see pretty good speedup (90 vs. 146 minutes).
By the way, you're not having anything else running are you ?
Things like X, an editor, etc. will gladly run on the spare CPU while
your simulation runs on one CPU. But with two simulations you will
actually see the performance hit.
You could boot in single-user mode, run the two simulations again,
and see if it makes a difference.
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