Messages in this thread |  | | Date | Thu, 6 Feb 1997 17:26:36 -0500 (EST) | From | Robert L Krawitz <> | Subject | Re: MMX performance.... |
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Date: Thu, 6 Feb 1997 16:21:48 -0600 (CST) From: Oliver Xymoron <oxymoron@waste.org> cc: submit-linux-dev-kernel@ratatosk.yggdrasil.com
> 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 bytes.
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 <rlk@tiac.net> http://www.tiac.net/users/rlk/
Member of the League for Programming Freedom -- mail lpf@uunet.uu.net Tall Clubs International -- http://www.tall.org/ or 1-800-521-2512
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