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All of the cores have to share the same front bus and northbridge.
The northbridge connects the cpu to memory and has limited bandwidth.
If several cores are running memory hungry applications, the front
buss will saturate.
The L2 cache helps for most applications, but not if you are burning
through a few G of quote data. The L2 cache is just 4-8MB.
The newer multi core systems have much faster front buses and that
trend is likely to continue.
So, it would be nice if AMI could support running multi cores, even
if it was just running different optimization passes on different
cores. That would saturate the front bus, but take advantage of all
of the memory bandwidth you have. It would really help those multi
day walkforward runs.
--- In amibroker@xxxxxxxxxxxxxxx, "markhoff" <markhoff@xxx> wrote:
>
>
> If you have a runtime penalty when running 2 independent AB jobs on
a
> Core Duo CPU it might be caused by too less memory (swapping to
disk)
> or other tasks which are also running (e.g. a web browser, audio
> streamer or whatever). You can check this with a process explorer
> which shows each tasks CPU utilisation. Similar, 4 AB jobs on a Core
> Quad should have nearly no penalty in runtime.
>
> Tomasz stated that multi-thread optimization does not scale good
with
> the CPU number, but it is not clear to me why this is the case. In
my
> understanding, AA optimization is a sequential process of running
the
> same AFL script with different parameters. If I have an AFL with
> significantly long runtime per optimization step (e.g. 1 minute) the
> overhead for the multi-threading should become quite small and
> independent tasks should scale nearly with the number of CPUs (as
long
> as there is sufficient memory, n threads might need n-times more
> memory than a single thread). For sure the situation is different if
> my single optimization run takes only a few millisecs or seconds,
then
> the overhead for multi-thread-managment goes up ...
>
> Maybe Tomasz can give some detailed comments on that issue?
>
> Best regards,
> Markus
>
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