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

Eric Dumazet
2021-11-25T06:35:05Z

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 !

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);