decrease L2 cache size used by Linux?

decrease L2 cache size used by Linux?

[Guerreiro da Luz]

Am benchmarking dumb matrix multiplication in trying to perceive
performance drop in case when matrix cannot fit in L2 cache.  However,
on my machine L2 cache is large - 2MB, so 512x512 matrix of double
numbers is needed to fill the cache, and in that case multiplication
is taking rather long time.  So I'm wondering is there a way to
control (decrease) L2 cache size used by Linux?  Apologies if question
inappropriate for the list.

Thanks.

Re: decrease L2 cache size used by Linux?

[Alan Cox]

> Am benchmarking dumb matrix multiplication in trying to perceive
> performance drop in case when matrix cannot fit in L2 cache.  However,
> on my machine L2 cache is large - 2MB, so 512x512 matrix of double
> numbers is needed to fill the cache, and in that case multiplication
> is taking rather long time.  So I'm wondering is there a way to
> control (decrease) L2 cache size used by Linux?  Apologies if question
> inappropriate for the list.

Not easily, but on the other hand if your process is taking a long time
you ought to get better and more reproducable results. Cache management
is mostly done by the processor not by the OS so you have little control
over pinning bits of it.

decrease L2 cache size used by Linux?

[Al Boldi]

Guerreiro da Luz wrote:
> Am benchmarking dumb matrix multiplication in trying to perceive
> performance drop in case when matrix cannot fit in L2 cache.  However,
> on my machine L2 cache is large - 2MB, so 512x512 matrix of double
> numbers is needed to fill the cache, and in that case multiplication
> is taking rather long time.  So I'm wondering is there a way to
> control (decrease) L2 cache size used by Linux?  Apologies if question
> inappropriate for the list.

You may want to turn off randomization,
 
echo 0 > /proc/sys/kernel/randomize_va_space
echo 1 > /proc/sys/vm/vdso_enabled

And see if that helps.


Thanks!

--
Al