Re: [tip:x86/core 1/1] arch/x86/um/../lib/csum-partial_64.c:98:12: error: implicit declaration of function 'load_unaligned_zeropad'

Noah Goldstein
2021-11-25T06:50:06Z

On Thu, Nov 25, 2021 at 12:32 AM Eric Dumazet <edumazet@google.com> wrote:
>
> On Wed, Nov 24, 2021 at 9:09 PM Noah Goldstein <goldstein.w.n@gmail.com> wrote:
> >
> >
> >
> > Although I see slightly worse performance with aligned `buff` in
> > the branch-free approach. Imagine if non-aligned `buff` is that
> > uncommon might be better to speculate past the work of `ror`.
>
> Yes, no clear win here removing the conditional (same cost really),
> although using a ror32() is removing the from32to16() helper and get
> rid of one folding.
>
> I will formally submit this change, thanks !

Great :)

Can you put me on the cc list? I have a patch for the function that I'll post
once yours gets through.

>
> diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c
> index 1eb8f2d11f7c785be624eba315fe9ca7989fd56d..cf4bd3ef66e56c681b3435d43011ece78438376d
> 100644
> --- a/arch/x86/lib/csum-partial_64.c
> +++ b/arch/x86/lib/csum-partial_64.c
> @@ -11,16 +11,6 @@
> #include <asm/checksum.h>
> #include <asm/word-at-a-time.h>
>
> -static inline unsigned short from32to16(unsigned a)
> -{
> - unsigned short b = a >> 16;
> - asm("addw %w2,%w0\n\t"
> - "adcw $0,%w0\n"
> - : "=r" (b)
> - : "0" (b), "r" (a));
> - return b;
> -}
> -
> /*
> * Do a checksum on an arbitrary memory area.
> * Returns a 32bit checksum.
> @@ -41,6 +31,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
> if (unlikely(odd)) {
> if (unlikely(len == 0))
> return sum;
> + temp64 = ror32((__force u32)sum, 8);
> temp64 += (*(unsigned char *)buff << 8);
> len--;
> buff++;
> @@ -129,10 +120,8 @@ __wsum csum_partial(const void *buff, int len, __wsum sum)
> #endif
> }
> result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff);
> - if (unlikely(odd)) {
> - result = from32to16(result);
> - result = ((result >> 8) & 0xff) | ((result & 0xff) << 8);
> - }
> + if (unlikely(odd))
> + result = ror32(result, 8);
> return (__force __wsum)result;
> }
> EXPORT_SYMBOL(csum_partial);