Re: [XenPPC] copy_page speedup using dcbz on target

[Hollis Blanchard <hollisb@xxxxxxxxxx>]

On Fri, 2006-12-15 at 17:50 -0500, poff wrote:
> > > 3) Useful when PPC must do page copies in place of 'page flipping'.
> >
> > So you're saying we should worry about it later?
> 
> 
> For the future, copy_page using dcbz:
> 
> diff -r 7669fca80bfc xen/arch/powerpc/mm.c
> --- a/xen/arch/powerpc/mm.c   Mon Dec 04 11:46:53 2006 -0500
> +++ b/xen/arch/powerpc/mm.c   Fri Dec 15 17:52:58 2006 -0500
> @@ -280,7 +280,8 @@ extern void copy_page(void *dp, void *sp
>      if (on_systemsim()) {
>          systemsim_memcpy(dp, sp, PAGE_SIZE);
>      } else {
> -        memcpy(dp, sp, PAGE_SIZE);
> +     clear_page(dp);
> +     __copy_page(dp, sp);
>      }
>  }
> 
> diff -r 7669fca80bfc xen/include/asm-powerpc/page.h
> --- a/xen/include/asm-powerpc/page.h  Mon Dec 04 11:46:53 2006 -0500
> +++ b/xen/include/asm-powerpc/page.h  Fri Dec 15 17:52:58 2006 -0500
> @@ -90,6 +90,25 @@ 1:  dcbz    0,%0\n\
> 
>  extern void copy_page(void *dp, void *sp);
> 
> +static __inline__ void __copy_page(void *dp, void *sp)
> +{
> +     ulong dwords, dword_size;
> +
> +     dword_size = 8;
> +     dwords = (PAGE_SIZE / dword_size) - 1;
> +
> +     __asm__ __volatile__(
> +     "mtctr  %2      # copy_page\n\
> +     ld      %2,0(%1)\n\
> +     std     %2,0(%0)\n\
> +1:   ldu     %2,8(%1)\n\
> +     stdu    %2,8(%0)\n\
> +     bdnz    1b"
> +     : /* no result */
> +     : "r" (dp), "r" (sp), "r" (dwords)
> +     : "%ctr", "memory");
> +}
> +

I'd rather have copy_page() dcbz; stdu; stdu; stdu; ... stdu; in each
loop iteration.

It would also be nice to improve memcpy, though that one is certainly
more difficult due to alignment, varying lengths, etc. Perhaps we can
borrow code from
http://penguinppc.org/dev/glibc/glibc-powerpc-cpu-addon.html

-- 
Hollis Blanchard
IBM Linux Technology Center


_______________________________________________
Xen-ppc-devel mailing list
Xen-ppc-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ppc-devel