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SubjectRe: FPU memcpy Penalty
Robert L Krawitz <rlk@tiac.net> writes:

[With regards to slow performance on "x11perf -putimage500" after applying
the Pentium memcpy patch:]

> >It might also be your video chip, BTW. It may not handle 64-bit
> >transfers (over the 32-bit PCI bus) very efficiently.
>
> Hmmm... I would guess that the X video transfers take place in
> user code in the X server, and are unaffected by the FPU memcpy patch.
> I assume the patch affects the transfers between the X client and
> server (with no SHM extension in use). I assume it affects lots of
> non-X system calls, and that might affect the timing!
>
>About the only thing it gets triggered for is page copies and the
>like. That was by intent. So this is an interesting mystery.

Unlike a pixmap which lives in the server, the image for XPutImage()
lives in the client address space and must be passed to the server
through the same bytestream as the rest of the protocol. That means
it's bouncing through the kernel.

Tom.



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