* [PATCH net-next] tcp: use likely() for srtt check in tcp_rtt_estimator()
@ 2026-08-08 11:00 Ziran Zhang
0 siblings, 0 replies; only message in thread
From: Ziran Zhang @ 2026-08-08 11:00 UTC (permalink / raw)
To: Eric Dumazet, Neal Cardwell, David S . Miller, Jakub Kicinski,
Paolo Abeni
Cc: Kuniyuki Iwashima, Simon Horman, netdev, linux-kernel,
Ziran Zhang
In tcp_rtt_estimator(), srtt is initialized to a non-zero value
after the first RTT measurement (srtt = m << 3) and never returns
to zero for the lifetime of the connection. Thus, the "srtt != 0"
branch is almost always true.
Marking it with likely() helps the compiler generate better code
for this hot path.
No functional change is introduced.
Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
net/ipv4/tcp_input.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 5b6378b94..a4c4d4760 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -1089,7 +1089,7 @@ static void tcp_rtt_estimator(struct sock *sk, long mrtt_us)
* does not matter how to _calculate_ it. Seems, it was trap
* that VJ failed to avoid. 8)
*/
- if (srtt != 0) {
+ if (likely(srtt != 0)) {
m -= (srtt >> 3); /* m is now error in rtt est */
srtt += m; /* rtt = 7/8 rtt + 1/8 new */
if (m < 0) {
--
2.51.0
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2026-08-08 11:00 [PATCH net-next] tcp: use likely() for srtt check in tcp_rtt_estimator() Ziran Zhang
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