Re: MMX performance....

Robert L Krawitz (
Thu, 6 Feb 1997 17:26:36 -0500 (EST)

Date: Thu, 6 Feb 1997 16:21:48 -0600 (CST)
From: Oliver Xymoron <>

> The Pentium memcpy() patch, BTW, has a lot of overhead of its own; it
> dumps and restores the FPU state (when it's in use it dumps the
> registers; when not, it dumps just the rest of the state). That's why
> it's configured to operate only when the amount of data to be copied
> is large. The overhead is well worth it, though, since memory
> bandwidth on write is used so much more efficiently.

What's the break-even copy size? Your patch seems to suggest 512 or 1024

It probably depends on the memory architecture. On my system (Neptune
mobo, 90 MHz, memory clocked at X-3-3-3) it wins even at 256 bytes. I
suspect with EDO it's a bit higher, in the 512-1024 byte range.

Robert Krawitz <> 

Member of the League for Programming Freedom -- mail Tall Clubs International -- or 1-800-521-2512