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Each time some payload is consumed by user space (recvmsg() and friends), TCP calls tcp_rcv_space_adjust() to run DRS algorithm to check if an increase of sk->sk_rcvbuf is needed. This function is based on time sampling, and currently calls tcp_mstamp_refresh(tp), which is a wrapper around ktime_get_ns(). ktime_get_ns() has a high cost on some platforms. 100+ cycles for rdtscp on AMD EPYC Turin for instance. We do not have to refresh tp->tcp_mpstamp, using the last cached value is enough. We only need to refresh it from __tcp_cleanup_rbuf() if an ACK must be sent (this is a rare event). Signed-off-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Kuniyuki Iwashima <kuniyu@google.com> Link: https://patch.msgid.link/20251024120707.3516550-1-edumazet@google.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>