[MPlayer-dev-eng] [RFC] disable fastmemcpy on x86-64 by default

[Reimar Döffinger]

Hello,
On Sun, May 27, 2007 at 07:29:09PM +0200, Michael Niedermayer wrote:
> On Sun, May 27, 2007 at 06:19:48PM +0200, Reimar D?ffinger wrote:
> > since SSE is part of the x86-64 architecture, at least glibc makes use
> > of it for its memcpy and some quick (and imprecise) tests indicate that
> > it's at least not slower.
> 
> TOOLS/fastmemcpybench.c ?

That does not help really much, since which one wins depends
extremely on sizes, e.g. (values in () are on 32 bit):

size 32 bytes:
system libc 1525.9MB/s (305.2MB/s)
fastmemcpy 381.5MB/s (339.1MB/s)

size 1024*768*2:
 1015.6MB/s (557.5MB/s)
 1201.6MB/s (1199.9MB/s)

for even larger sizes the differences don't seem to be statistically
relevant.

In personally don't find the difference decidedly enough in favour for
our fastmemcpy to use it in my own builds but your opinion might
differ (using system memcpy reduces binary size and instruction cache
load)...

Greetings,
Reimar Döffinger