lkml.org 
[lkml]   [2001]   [Dec]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [patch] Prefetching file_read_actor()
Date
On December 31, 2001 11:47, Dave Jones wrote:
> Completly puzzled right now. Moving the prefetching to copy_to_user
> (and doing the tlb preload & prefetching the whole chunk to be copied
> (or cachesize if smaller)) results in a performance drop instead of a win.
>
> My initial guess is that some of the callers of copy_to_user are
> doing something that is harmed the prefetching.
> (Maybe they are doing additional prefetch() calls)

Maybe syscalls that only have to move a very small chunk of data
(gettimeofday(2), for instance), are hurt because of the wasted bytes they
are prefetching after the intended data? Also, for sizes greater than 512,
copy_to_user will call mmx_copy_user, which might call mmx_memcpy, which does
prefetching already on x86 CPUs that support it.

-Ryan
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:18    [W:0.084 / U:6.324 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site