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tcp: reduce calls to tcp_schedule_loss_probe()

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For RPC workloads, we alternate tcp_schedule_loss_probe() calls from
output path and from input path, with tp->packets_out value
oscillating between !zero and zero, leading to poor branch prediction.

Move tp->packets_out check from tcp_schedule_loss_probe() to
tcp_set_xmit_timer().

We avoid one call to tcp_schedule_loss_probe() from tcp_ack()
path for typical RPC workloads, while improving branch prediction.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com>
Link: https://patch.msgid.link/20260223113501.4070245-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Eric Dumazet
2026-02-24 17:44:33 -08:00
committed by Jakub Kicinski
parent a09eb622f3
commit fca59a2dd0
2 changed files with 2 additions and 2 deletions
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net/ipv4/tcp_input.c
+1 -1
View File
@@ -3552,7 +3552,7 @@ void tcp_rearm_rto(struct sock *sk)
/* Try to schedule a loss probe; if that doesn't work, then schedule an RTO. */
static void tcp_set_xmit_timer(struct sock *sk)
{
if (!tcp_schedule_loss_probe(sk, true))
if (!tcp_sk(sk)->packets_out || !tcp_schedule_loss_probe(sk, true))
tcp_rearm_rto(sk);
}
net/ipv4/tcp_output.c
+1 -1
View File
@@ -3135,7 +3135,7 @@ bool tcp_schedule_loss_probe(struct sock *sk, bool advancing_rto)
* not in loss recovery, that are either limited by cwnd or application.
*/
if ((early_retrans != 3 && early_retrans != 4) ||
!tp->packets_out || !tcp_is_sack(tp) ||
!tcp_is_sack(tp) ||
(icsk->icsk_ca_state != TCP_CA_Open &&
icsk->icsk_ca_state != TCP_CA_CWR))
return false;