Messages in this thread | | | From | David Laight <> | Subject | RE: x86/csum: Remove unnecessary odd handling | Date | Wed, 6 Sep 2023 13:49:24 +0000 |
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From: Noah Goldstein > Sent: 01 September 2023 23:21 > > The special case for odd aligned buffers is unnecessary and mostly > just adds overhead. Aligned buffers is the expectations, and even for > unaligned buffer, the only case that was helped is if the buffer was > 1-byte from word aligned which is ~1/7 of the cases. Overall it seems > highly unlikely to be worth to extra branch. > > It was left in the previous perf improvement patch because I was > erroneously comparing the exact output of `csum_partial(...)`, but > really we only need `csum_fold(csum_partial(...))` to match so its > safe to remove.
This is pretty much the same patch I send in Dec 2021...
Reviewed-by: David Laight <david.laight@aculab.com>
> > All csum kunit tests pass. > > Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com> > Reviewed-by: Eric Dumazet <edumazet@google.com> > --- > arch/x86/lib/csum-partial_64.c | 37 ++-------------------------------- > 1 file changed, 2 insertions(+), 35 deletions(-) > > diff --git a/arch/x86/lib/csum-partial_64.c b/arch/x86/lib/csum-partial_64.c > index cea25ca8b8cf..d06112e98893 100644 > --- a/arch/x86/lib/csum-partial_64.c > +++ b/arch/x86/lib/csum-partial_64.c > @@ -11,28 +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; > -} > - > -static inline __wsum csum_tail(u64 temp64, int odd) > -{ > - unsigned int result; > - > - result = add32_with_carry(temp64 >> 32, temp64 & 0xffffffff); > - if (unlikely(odd)) { > - result = from32to16(result); > - result = ((result >> 8) & 0xff) | ((result & 0xff) << 8); > - } > - return (__force __wsum)result; > -} > - > /* > * Do a checksum on an arbitrary memory area. > * Returns a 32bit checksum. > @@ -47,17 +25,6 @@ static inline __wsum csum_tail(u64 temp64, int odd) > __wsum csum_partial(const void *buff, int len, __wsum sum) > { > u64 temp64 = (__force u64)sum; > - unsigned odd; > - > - odd = 1 & (unsigned long) buff; > - if (unlikely(odd)) { > - if (unlikely(len == 0)) > - return sum; > - temp64 = ror32((__force u32)sum, 8); > - temp64 += (*(unsigned char *)buff << 8); > - len--; > - buff++; > - } > > /* > * len == 40 is the hot case due to IPv6 headers, but annotating it likely() > @@ -73,7 +40,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum) > "adcq $0,%[res]" > : [res] "+r"(temp64) > : [src] "r"(buff), "m"(*(const char(*)[40])buff)); > - return csum_tail(temp64, odd); > + return add32_with_carry(temp64 >> 32, temp64 & 0xffffffff); > } > if (unlikely(len >= 64)) { > /* > @@ -143,7 +110,7 @@ __wsum csum_partial(const void *buff, int len, __wsum sum) > : [res] "+r"(temp64) > : [trail] "r"(trail)); > } > - return csum_tail(temp64, odd); > + return add32_with_carry(temp64 >> 32, temp64 & 0xffffffff); > } > EXPORT_SYMBOL(csum_partial); > > -- > 2.34.1
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