On Mon, Apr 14, 2025 at 03:13:05PM +0200, chia-yu.chang@nokia-bell-labs.com wrote:
From: Ilpo Järvinen ij@kernel.org
These counters track IP ECN field payload byte sums for all arriving (acceptable) packets. The AccECN option (added by a later patch in the series) echoes these counters back to sender side.
Signed-off-by: Ilpo Järvinen ij@kernel.org Signed-off-by: Neal Cardwell ncardwell@google.com Signed-off-by: Chia-Yu Chang chia-yu.chang@nokia-bell-labs.com
include/linux/tcp.h | 1 + include/net/tcp.h | 18 +++++++++++++++++- net/ipv4/tcp.c | 3 ++- net/ipv4/tcp_input.c | 13 +++++++++---- net/ipv4/tcp_minisocks.c | 3 ++- 5 files changed, 31 insertions(+), 7 deletions(-)
diff --git a/include/linux/tcp.h b/include/linux/tcp.h index af38fff24aa4..9cbfefd693e3 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h @@ -303,6 +303,7 @@ struct tcp_sock { u32 delivered; /* Total data packets delivered incl. rexmits */ u32 delivered_ce; /* Like the above but only ECE marked packets */ u32 received_ce; /* Like the above but for rcvd CE marked pkts */
- u32 received_ecn_bytes[3]; u8 received_ce_pending:4, /* Not yet transmit cnt of received_ce */ unused2:4; u32 app_limited; /* limited until "delivered" reaches this val */
...
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 73f8cc715bff..278990dba721 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -5092,6 +5092,7 @@ static void __init tcp_struct_check(void) CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, delivered); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, delivered_ce); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, received_ce);
- CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, received_ecn_bytes); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, app_limited); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rcv_wnd); CACHELINE_ASSERT_GROUP_MEMBER(struct tcp_sock, tcp_sock_write_txrx, rx_opt);
@@ -5099,7 +5100,7 @@ static void __init tcp_struct_check(void) /* 32bit arches with 8byte alignment on u64 fields might need padding * before tcp_clock_cache. */
- CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 97 + 7);
- CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 109 + 3);
Hi Ilpo,
I think that incrementing 97 to 109 is correct, as 12 bytes have been added to this group.
However, I do not think it is correct to decrement 7 to 3.
On, at least, x86_64, x86_32 and arm64 that decrement does not cause any problems. (I assume it is also fine without the rest of this patch).
But on (32-bit) ARM, this causes the assertion to fail. This is because on ARM an extra 4-byte hole is added just after pred_flags. And the assertion checks an upper bound on the size of the group.
I assume this extra hole is due to alignment requirements. In any case on ARM, with this patch applied, pahole shows the group looking like this:
__u8 __cacheline_group_begin__tcp_sock_write_txrx[0]; /* 1869 0 */
/* XXX 3 bytes hole, try to pack */
__be32 pred_flags; /* 1872 4 */
/* XXX 4 bytes hole, try to pack */
u64 tcp_clock_cache; /* 1880 8 */ u64 tcp_mstamp; /* 1888 8 */ u32 rcv_nxt; /* 1896 4 */ u32 snd_nxt; /* 1900 4 */ u32 snd_una; /* 1904 4 */ u32 window_clamp; /* 1908 4 */ u32 srtt_us; /* 1912 4 */ u32 packets_out; /* 1916 4 */ /* --- cacheline 30 boundary (1920 bytes) --- */ u32 snd_up; /* 1920 4 */ u32 delivered; /* 1924 4 */ u32 delivered_ce; /* 1928 4 */ u32 received_ce; /* 1932 4 */ u32 received_ecn_bytes[3]; /* 1936 12 */ u8 received_ce_pending:4; /* 1948: 0 1 */ u8 unused2:4; /* 1948: 4 1 */
/* XXX 3 bytes hole, try to pack */
u32 app_limited; /* 1952 4 */ u32 rcv_wnd; /* 1956 4 */ struct tcp_options_received rx_opt; /* 1960 24 */ /* --- cacheline 31 boundary (1984 bytes) --- */ u8 nonagle:4; /* 1984: 0 1 */ u8 rate_app_limited:1; /* 1984: 4 1 */
/* XXX 3 bits hole, try to pack */
__u8 __cacheline_group_end__tcp_sock_write_txrx[0]; /* 1985 0 */
So we are now at 3 cache lines. And perhaps it is worth trying to pack things a bit. Or perhaps that becomes tricky to get right across different architectures. I didn't explore that.
But, taking the naive approach: with the following update, tcp.c compiles compiles with allmodconfig on x86_64, x86_32, ARM and arm64 (I did not test others).
CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 109 + 7);
For the record, gcc 14.2.0 reports this problem as:
CC net/ipv4/tcp.o In file included from <command-line>: In function 'tcp_struct_check', inlined from 'tcp_init' at net/ipv4/tcp.c:5133:2: ././include/linux/compiler_types.h:557:45: error: call to '__compiletime_assert_ 1403' declared with attribute error: BUILD_BUG_ON failed: offsetof(struct tcp_sock, __cacheline_group_end__tcp_sock_write_txrx) - offsetofend(struct tcp_sock, __cacheline_group_begin__tcp_sock_write_txrx) > 109 + 3 557 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^ ././include/linux/compiler_types.h:538:25: note: in definition of macro '__compiletime_assert' 538 | prefix ## suffix(); \ | ^~~~~~ ././include/linux/compiler_types.h:557:9: note: in expansion of macro '_compiletime_assert' 557 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__) | ^~~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert' 39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg) | ^~~~~~~~~~~~~~~~~~ ./include/linux/build_bug.h:50:9: note: in expansion of macro 'BUILD_BUG_ON_MSG' 50 | BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition) | ^~~~~~~~~~~~~~~~ ./include/linux/cache.h:160:9: note: in expansion of macro 'BUILD_BUG_ON' 160 | BUILD_BUG_ON(offsetof(TYPE, __cacheline_group_end__##GROUP) - \ | ^~~~~~~~~~~~ net/ipv4/tcp.c:5103:9: note: in expansion of macro 'CACHELINE_ASSERT_GROUP_SIZE' 5103 | CACHELINE_ASSERT_GROUP_SIZE(struct tcp_sock, tcp_sock_write_txrx, 109 + 3); | ^~~~~~~~~~~~~~~~~~~~~~~~~~~
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