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Message-ID: <176763908096.510.3138878419623948783.tip-bot2@tip-bot2>
Date: Mon, 05 Jan 2026 18:51:20 -0000
From: "tip-bot2 for Eric Dumazet" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Eric Dumazet <edumazet@...gle.com>,
Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
linux-kernel@...r.kernel.org
Subject: [tip: x86/misc] x86/lib: Inline csum_ipv6_magic()
The following commit has been merged into the x86/misc branch of tip:
Commit-ID: 529676cabcf4a5046d217bba2c8f3b94a3f6a10f
Gitweb: https://git.kernel.org/tip/529676cabcf4a5046d217bba2c8f3b94a3f6a10f
Author: Eric Dumazet <edumazet@...gle.com>
AuthorDate: Thu, 13 Nov 2025 15:45:45
Committer: Dave Hansen <dave.hansen@...ux.intel.com>
CommitterDate: Mon, 05 Jan 2026 10:14:05 -08:00
x86/lib: Inline csum_ipv6_magic()
Inline this small helper. It has been observed to consume up
to 0.75%, which is significant for such a small function.
This should reduce register pressure, as saddr and daddr are often
back to back in memory.
For instance code inlined in tcp6_gro_receive() will look like:
55a: 48 03 73 28 add 0x28(%rbx),%rsi
55e: 8b 43 70 mov 0x70(%rbx),%eax
561: 29 f8 sub %edi,%eax
563: 0f c8 bswap %eax
565: 89 c0 mov %eax,%eax
567: 48 05 00 06 00 00 add $0x600,%rax
56d: 48 03 46 08 add 0x8(%rsi),%rax
571: 48 13 46 10 adc 0x10(%rsi),%rax
575: 48 13 46 18 adc 0x18(%rsi),%rax
579: 48 13 46 20 adc 0x20(%rsi),%rax
57d: 48 83 d0 00 adc $0x0,%rax
581: 48 89 c6 mov %rax,%rsi
584: 48 c1 ee 20 shr $0x20,%rsi
588: 01 f0 add %esi,%eax
58a: 83 d0 00 adc $0x0,%eax
58d: 89 c6 mov %eax,%esi
58f: 66 31 c0 xor %ax,%ax
Surprisingly, this inlining does not seem to bloat kernel text size.
It at least two cases[1], it either has no effect or results in a
slightly smaller kernel.
1. https://lore.kernel.org/all/CANn89iJzcb_XO9oCApKYfRxsMMmg7BHukRDqWTca3ZLQ8HT0iQ@mail.gmail.com/
[ dhansen: add justification and note about lack of kernel bloat ]
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Acked-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://patch.msgid.link/20251113154545.594580-1-edumazet@google.com
---
arch/x86/include/asm/checksum_64.h | 45 +++++++++++++++++++++--------
arch/x86/lib/csum-wrappers_64.c | 22 +--------------
2 files changed, 33 insertions(+), 34 deletions(-)
diff --git a/arch/x86/include/asm/checksum_64.h b/arch/x86/include/asm/checksum_64.h
index 4d4a47a..5bdfd2d 100644
--- a/arch/x86/include/asm/checksum_64.h
+++ b/arch/x86/include/asm/checksum_64.h
@@ -9,6 +9,7 @@
*/
#include <linux/compiler.h>
+#include <linux/in6.h>
#include <asm/byteorder.h>
/**
@@ -145,6 +146,17 @@ extern __wsum csum_partial_copy_nocheck(const void *src, void *dst, int len);
*/
extern __sum16 ip_compute_csum(const void *buff, int len);
+static inline unsigned add32_with_carry(unsigned a, unsigned b)
+{
+ asm("addl %2,%0\n\t"
+ "adcl $0,%0"
+ : "=r" (a)
+ : "0" (a), "rm" (b));
+ return a;
+}
+
+#define _HAVE_ARCH_IPV6_CSUM 1
+
/**
* csum_ipv6_magic - Compute checksum of an IPv6 pseudo header.
* @saddr: source address
@@ -158,20 +170,29 @@ extern __sum16 ip_compute_csum(const void *buff, int len);
* Returns the unfolded 32bit checksum.
*/
-struct in6_addr;
+static inline __sum16 csum_ipv6_magic(
+ const struct in6_addr *_saddr, const struct in6_addr *_daddr,
+ __u32 len, __u8 proto, __wsum sum)
+{
+ const unsigned long *saddr = (const unsigned long *)_saddr;
+ const unsigned long *daddr = (const unsigned long *)_daddr;
+ __u64 sum64;
-#define _HAVE_ARCH_IPV6_CSUM 1
-extern __sum16
-csum_ipv6_magic(const struct in6_addr *saddr, const struct in6_addr *daddr,
- __u32 len, __u8 proto, __wsum sum);
+ sum64 = (__force __u64)htonl(len) + (__force __u64)htons(proto) +
+ (__force __u64)sum;
-static inline unsigned add32_with_carry(unsigned a, unsigned b)
-{
- asm("addl %2,%0\n\t"
- "adcl $0,%0"
- : "=r" (a)
- : "0" (a), "rm" (b));
- return a;
+ asm(" addq %1,%[sum64]\n"
+ " adcq %2,%[sum64]\n"
+ " adcq %3,%[sum64]\n"
+ " adcq %4,%[sum64]\n"
+ " adcq $0,%[sum64]\n"
+
+ : [sum64] "+r" (sum64)
+ : "m" (saddr[0]), "m" (saddr[1]),
+ "m" (daddr[0]), "m" (daddr[1]));
+
+ return csum_fold(
+ (__force __wsum)add32_with_carry(sum64 & 0xffffffff, sum64>>32));
}
#define HAVE_ARCH_CSUM_ADD
diff --git a/arch/x86/lib/csum-wrappers_64.c b/arch/x86/lib/csum-wrappers_64.c
index f4df4d2..831b711 100644
--- a/arch/x86/lib/csum-wrappers_64.c
+++ b/arch/x86/lib/csum-wrappers_64.c
@@ -68,25 +68,3 @@ csum_partial_copy_nocheck(const void *src, void *dst, int len)
}
EXPORT_SYMBOL(csum_partial_copy_nocheck);
-__sum16 csum_ipv6_magic(const struct in6_addr *saddr,
- const struct in6_addr *daddr,
- __u32 len, __u8 proto, __wsum sum)
-{
- __u64 rest, sum64;
-
- rest = (__force __u64)htonl(len) + (__force __u64)htons(proto) +
- (__force __u64)sum;
-
- asm(" addq (%[saddr]),%[sum]\n"
- " adcq 8(%[saddr]),%[sum]\n"
- " adcq (%[daddr]),%[sum]\n"
- " adcq 8(%[daddr]),%[sum]\n"
- " adcq $0,%[sum]\n"
-
- : [sum] "=r" (sum64)
- : "[sum]" (rest), [saddr] "r" (saddr), [daddr] "r" (daddr));
-
- return csum_fold(
- (__force __wsum)add32_with_carry(sum64 & 0xffffffff, sum64>>32));
-}
-EXPORT_SYMBOL(csum_ipv6_magic);
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