Re: [XenPPC] PATCH: Inline assembler for clear_page() and copy_page()

[Jimi Xenidis <jimix@xxxxxxxxxxxxxx>]

On Aug 25, 2006, at 5:48 PM, poff@xxxxxxxxxxxxxx wrote:

> note2: in page_alloc.c, one of the three clear_page() calls breaks  
> the system
> when changed to clear_page_cacheable().
I suspected why this was troubleseme, but I was wrong, can you give  
us a reason why you think it is?
Off to the code...
Since everything is caches I'll ignore the non-cacheable versions and  
only consider the cacheable versions.
> +static __inline__ void copy_page(void *dp, void *sp)
[ignore]

> +/* assumes page, *addr, is cacheable */
> +static __inline__ void clear_page_cacheable(void *addr)
EVERYTHING is cacheable.
  +static __inline__ void clear_page(void *addr)
> +{
> +       unsigned long lines, line_size;
> +
> +       line_size = CACHE_LINE_SIZE;
This should really be a function defined in arch/powerpc/powerpc64/ 
ppc970.c
maybe something like cpu_cache_line_size(), or at some point we  
should prolly have a struct cpu_info that contains all this stuff  
rather than make a call for this stuff all the time.
Tho I think Hollis and I will have to debate this one :)

> +/* assumes destination page, *dp, is cacheable */
> +static __inline__ void copy_page_cacheable(void *dp, void *sp)
+static __inline__ void copy_page(void *dp, void *sp)
> +{
> +       unsigned long dwords, dword_size;
> +
> +       dword_size = 8;
> +       dwords = (PAGE_SIZE / dword_size) - 1;
> +
> +       clear_page_cacheable(dp);
why the clear?
If your intent was to clear the cache line to avoid read-modify- 
write, then integrating it into the loop would have a much bigger  
effect.
> +
> +       __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)
Nt 100% sure on this, but since, at the end of your assembler you are  
changing %0-%2 the should be "=r" in the output area or in the  
clobber list.
> +       : "%ctr", "memory");
> +}
-JX




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