Re: [PATCH] add a clear_pages function to clear pages of higher order

From: Denis Vlasenko
Date: Fri Mar 11 2005 - 03:09:50 EST

On Friday 11 March 2005 03:03, Christoph Lameter wrote:
> Changelog:
> - use Kconfig and CONFIG_CLEAR_PAGES
> The zeroing of a page of a arbitrary order in page_alloc.c and in hugetlb.c may benefit from a
> clear_page that is capable of zeroing multiple pages at once. The following patch adds
> a function "clear_pages" that is capable of clearing multiple continuous pages at once.
> Patch against 2.6.11-bk6
> Signed-off-by: Christoph Lameter <clameter@xxxxxxx>
> -clear_page_end:
> +clear_pages_end:
> /* C stepping K8 run faster using the string instructions.
> It is also a lot simpler. Use this when possible */

Andi Kleen (iirc) says that non-temporal stores seem to be
big win in microbenchmarks (and I second that), but they are
a net loss when we are going to use zeroed page just after
zeroing. He recommends avoid using non-temporal stores

With this new page prezeroing infrastructure, that argument
most likely is not right anymore. Especially clearing of
high-order pages definitely will benefit from NT stores
because they do not kill L1 data cache in the process.

I don't have K8 and therefore cannot be 100% sure, but
I really doubt that K8 optimize "rep stosq" into _NT_ stores.


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