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| author | Eric Dumazet <edumazet@google.com> | 2014-03-23 19:51:36 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-03-24 00:18:44 -0400 |
| commit | 99f0b958b194f7d88973f1c2190d207e0a2c7e79 (patch) | |
| tree | f76073a45af1840a773084b039c53f7b7db58fb5 /include/net | |
| parent | 860b4042ddec744de52461f91c869630b1bb23c2 (diff) | |
| download | linux-99f0b958b194f7d88973f1c2190d207e0a2c7e79.tar.bz2 | |
net: optimize csum_replace2()
When changing one 16bit value by another in IP header, we can adjust
the IP checksum by doing a simple operation described in RFC 1624, as
reminded by David.
csum_partial() is a complex function on x86_64, not really suited for
small number of checksummed bytes.
I spotted csum_partial() being in the top 20 most consuming functions
(more than 1 %) in a GRO workload, which was rather unexpected.
The caller was inet_gro_complete() doing a csum_replace2() when
building the new IP header for the GRO packet.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net')
| -rw-r--r-- | include/net/checksum.h | 23 |
1 files changed, 21 insertions, 2 deletions
diff --git a/include/net/checksum.h b/include/net/checksum.h index 37a0e24adbe7..a28f4e0f6251 100644 --- a/include/net/checksum.h +++ b/include/net/checksum.h @@ -69,6 +69,19 @@ static inline __wsum csum_sub(__wsum csum, __wsum addend) return csum_add(csum, ~addend); } +static inline __sum16 csum16_add(__sum16 csum, __be16 addend) +{ + u16 res = (__force u16)csum; + + res += (__force u16)addend; + return (__force __sum16)(res + (res < (__force u16)addend)); +} + +static inline __sum16 csum16_sub(__sum16 csum, __be16 addend) +{ + return csum16_add(csum, ~addend); +} + static inline __wsum csum_block_add(__wsum csum, __wsum csum2, int offset) { @@ -112,9 +125,15 @@ static inline void csum_replace4(__sum16 *sum, __be32 from, __be32 to) *sum = csum_fold(csum_partial(diff, sizeof(diff), ~csum_unfold(*sum))); } -static inline void csum_replace2(__sum16 *sum, __be16 from, __be16 to) +/* Implements RFC 1624 (Incremental Internet Checksum) + * 3. Discussion states : + * HC' = ~(~HC + ~m + m') + * m : old value of a 16bit field + * m' : new value of a 16bit field + */ +static inline void csum_replace2(__sum16 *sum, __be16 old, __be16 new) { - csum_replace4(sum, (__force __be32)from, (__force __be32)to); + *sum = ~csum16_add(csum16_sub(~(*sum), old), new); } struct sk_buff; |