Re: [rfc][patch] store-free path walking

Denys Vlasenko
2009-10-08T13:12:48Z

On Wed, Oct 7, 2009 at 11:57 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> This, btw, is exactly the kind of thing we saw with some of the
> non-temporal work, when we used nontemporal stores to copy pages on COW
> faults, or when doing pre-zeroing of pages. You get rid of some of the
> hot-spots in the kernel, and you then replace them with user space taking
> the cache misses in random spots instead. The kernel profile looks better,
> and system time may go down, but actual performace never went down - you
> just moved your cache miss cost from one place to another.

A few years ago when K7s were not ancient yet, after hearing
argument for and against non-temporal stores,
I decided to finally figure it for myself.

I tested kernel build workload on two kernels with the only
one difference - clear_page with and without non-temporal stores.

"Non-temporal stores" kernel was faster, not slower. Just a little bit,
but reproducibly.
--
vda