Re: A factoring algorithm


Chris Card wrote:
> Phil Carmody wrote:
> > You can tell if a the memory used in a critical part of your code
> > is in the L1 cache by using performance monitoring counters, assuming
> > your processor has such a feature. Just set them up to count memory
> > accesses (or L1 hits) and L1 misses.
> I have read the Intel documentation for my processor (Pentium 4), and I
> can see in principle how to do this - program the counters using the
> WDMSR instruction, and
> read the values using the RDPMC instruction. However, how do you do it
> in practice?
> The WDMSR instruction can only be executed in the kernel as far as I
> can see, so how do I program the counters using an application running
> on Windows XP?
> And since it looks hard work to write the code, does anyone have any
> code available for this?

You need a kernel driver. Tools like Intel Vtune and AMD CodeAnalyst
(as well as our internal tools) do this regularly. In Linux a kernel
module has the correct privileges.

How you write kernel drivers/modules is another discussion altogether.


Tom

.

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