Re: copy_user_page_asm suggested 64bit improvment [Was: [parisc-linux] clear user page test]

[Grant Grundler <grundler@parisc-linux.org>]

On Fri, Dec 31, 2004 at 02:26:13PM -0600, Michael S. Zick wrote:
>     This path should not be within the set of user observable execution times.
...
> NOTE: Zeroing a page on return to (any) free pool is not 'user observable' only
> the 'add to free pool incoming queue' is in the 'user observable' code path.
> 
> NOTE: Pages handled by this daemon may have both d-cache and i-cache
> representations.  But the code which deals with this situation is not 'user 
> observable' because the entire 'return to free pool' operation is not 'user
> observable'.
...
> Q.E.D: Zeroing a page with the destination of user space assignment need not
> be a 'user observable' execution time.

Mike,
The copy_user_page and zero_page functions *are* observable since they
affect metrics reported by "time" and readprofile. I don't care if they
are in invoked in the application context or some other context.

Certainly, it would reduce startup latency to pre-zero the pages in
the kernel (daemon) and have them ready when apps want them.
But on a loaded system, I expect this will be slightly less efficient
and more complex since one doesn't know how many need to be pre-zero'd
or when to steal pre-zero'd pages for other uses (e.g. load in an
executable).

> There should be additional gains made in 'copy-[to|from]-user' when these four
> conditions are enforced.

I read the conditions and thought "neat".
I don't pretend to understand all of them or what they mean.
But instead of trying to explain them, could you send me a patch that works?
Maybe something that has a chance of going back upstream to linus?

thanks,
grant

> 
> Mike
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