diff mbox series

[net-next,1/2] gro: optimize skb_gro_postpull_rcsum()

Message ID 20211124202446.2917972-2-eric.dumazet@gmail.com (mailing list archive)
State Accepted
Commit 0bd28476f6363c7ccc841fe6a0ab0dd1fdb822f6
Delegated to: Netdev Maintainers
Headers show
Series net: small csum optimizations | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Series has a cover letter
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 20 this patch: 20
netdev/cc_maintainers success CCed 3 of 3 maintainers
netdev/build_clang success Errors and warnings before: 22 this patch: 22
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 24 this patch: 24
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 10 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Eric Dumazet Nov. 24, 2021, 8:24 p.m. UTC 
From: Eric Dumazet <edumazet@google.com>

We can leverage third argument to csum_partial():

  X = csum_sub(X, csum_partial(start, len, 0));

  -->

  X = csum_add(X, ~csum_partial(start, len, 0));

  -->

  X = ~csum_partial(start, len, ~X);

This removes one add/adc pair and its dependency against the carry flag.

Signed-off-by: Eric Dumazet <edumazet@google.com>
---
 include/net/gro.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/include/net/gro.h b/include/net/gro.h
index 9c22a010369cb89f9511d78cc322be56170d7b20..b1139fca7c435ca0c353c4ed17628dd7f3df4401 100644
--- a/include/net/gro.h
+++ b/include/net/gro.h
@@ -173,8 +173,8 @@  static inline void skb_gro_postpull_rcsum(struct sk_buff *skb,
 					const void *start, unsigned int len)
 {
 	if (NAPI_GRO_CB(skb)->csum_valid)
-		NAPI_GRO_CB(skb)->csum = csum_sub(NAPI_GRO_CB(skb)->csum,
-						  csum_partial(start, len, 0));
+		NAPI_GRO_CB(skb)->csum = ~csum_partial(start, len,
+						       ~NAPI_GRO_CB(skb)->csum);
 }
 
 /* GRO checksum functions. These are logical equivalents of the normal