Re: [RFC] [PATCH] cache pollution aware __copy_from_user_ll()

Akira Tsukamoto
2005-08-17T15:20:50Z

I am resubmitting this because it seems to be lost when I posted
the before yesterday.

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Arjan van de Ven mentioned:
> The only comment/question I have is about the use of prefetchnta; that
> might have cache-evicting properties as well (eg evict the cache of the
> original of the copy, eg the userspace memory). Is that really the right
> approach?
> In addition, my measurements show that removing the prefetch from the
> main copy loop is a gain because the modern cpus have an autoprefetcher
> already in the hardware.

My computer with Athlon K7 was faster with manually prefetching,
but I did not know it is already becoming obsolete.

It was pretty while ago, but I also made a similar copy_user function;
http://www.suna-asobi.com/~akira-t/linux/k7-copy-user/K7-copy-47.patch
I add comments on each item in the copy function. It was basically
inspired from Takahashi's intel faster copy function.

I also have some explanation about the speedup for pipelined cpu.
http://www.suna-asobi.com/~akira-t/linux/k7-copy-user/copy_for_highlypipelined_cpu.txt

It was originally discussed in this thread,