Re: Fw: framebuffer blitting performance loss 2.6.12 -> 2.6.13-rc3

Il Fri, Jul 29, 2005 at 08:51:34PM +0100, James Simmons ha scritto: 

quoted

Thank you for your persistence.  I think I know the culprit.  Someone
insisted on using memcpy in fb_pad_aligned_buffer().  I have already
fixed this before, but apparently, the memcpy was brought back.  Try
the attached patch and let me know.

Yipes, I did that. The memcpy function is suppose to be optimized for the 
platform. See string.h in the include/asm directory. I seen for example 
the Athlon would use the 3DNow instruction set to copy data. Something 
is really wrong with memcpy if moving byte by byte is faster !!!! 

For small copies MMX/3DNow are not used at all. In current kernel
MMX/3DNow memcpy is used only when data size is greater than 512bytes.
Remember that MMX/3DNow uses FPU so the kernel must save/restore state
and this overhead would make the copy slow for small chunks.

Luca
-- 
Home: http://kronoz.cjb.net
Se il  destino di un uomo  e` annegare, anneghera` anche  in un bicchier
d'acqua.
Proverbio yddish


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