From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-m16.yeah.net (mail-m16.yeah.net [1.95.21.15]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id A60191C84BC; Sat, 8 Aug 2026 11:02:32 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=1.95.21.15 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786186958; cv=none; b=X2V3Zi/BLmX3v/wuBnpoL118oV4jJUV6gYh4nViJ/PHNFC6D6mrf6YYQujkvJoeEAHbzNe972N2pcTQXugqPi4VytW6nA6Cl6P1arW4YNyqszHT2HOgpPhPbiZz57mm2E7HjDOu8kt89eXuRRf0aUqaPU3GA8jN4pc8ZIq5XVT4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786186958; c=relaxed/simple; bh=ZX8DEm/tchk9zoG5qv++1CkRgB9/GbbbuxDx75UCUZQ=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version; b=hWt2VMOunXpMUCHuoMB2Ixpll9r8HM2ANXU+tGJJnLHxQAH482yRC1arxyzxEH2BB26nGilZJY+adZh2nS3xwPnHbUhV/0XBO+/vOr8dkeuWdOjTXBVlanHBf0boVCzwDfax+xpwuYn4S66rG336VjPENOhbKC4v3FzQzKaFIcA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yeah.net; spf=pass smtp.mailfrom=yeah.net; dkim=pass (1024-bit key) header.d=yeah.net header.i=@yeah.net header.b=hlzng+hb; arc=none smtp.client-ip=1.95.21.15 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=yeah.net Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=yeah.net Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=yeah.net header.i=@yeah.net header.b="hlzng+hb" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=yeah.net; s=s110527; h=From:To:Subject:Date:Message-ID:MIME-Version; bh=6E EFqsqlqUNUW19mDTieOJor4R28eegdtmINXcoUzDw=; b=hlzng+hbpucpkxEkeP jedZ+5NoB3Mp+p4GJSbwuNnxhBWsgul2CE504Uye6NPfiT7EuGxsyb61WczMPt+8 einbRaXrO9kuFr1o3km/aip8BZpWVO9bZ95/4fqQORnF45Co/cCtaiOlN6B8kIIZ Xl80YcMw/AyK0y1KJd7DqCGmw= Received: from deepin (unknown []) by gzsmtp2 (Coremail) with UTF8SMTPSA id Ms8vCgD3HRZyDHdq7Y1xAw--.25025S4; Sat, 08 Aug 2026 19:01:43 +0800 (CST) From: Ziran Zhang To: Eric Dumazet , Neal Cardwell , "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: Kuniyuki Iwashima , Simon Horman , netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Ziran Zhang Subject: [PATCH net-next] tcp: use likely() for srtt check in tcp_rtt_estimator() Date: Sat, 8 Aug 2026 19:00:54 +0800 Message-ID: <20260808110054.6892-1-zhangcoder@yeah.net> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID:Ms8vCgD3HRZyDHdq7Y1xAw--.25025S4 X-Coremail-Antispam: 1Uf129KBjvdXoWrtFy3Kry3ZrykWrWfWr4Uurg_yoWfKrgEka s29a1kuw4xXr4xZF4DZw4Ygwn8GrZ3JFyfCr1fJFWUK34UJan8Can2kr9rZrnY9rsrGrZ8 Arn5WFy5ZryI9jkaLaAFLSUrUUUUjb8apTn2vfkv8UJUUUU8Yxn0WfASr-VFAUDa7-sFnT 9fnUUvcSsGvfC2KfnxnUUI43ZEXa7xR_UUUUUUUUU== X-CM-SenderInfo: x2kd0wpfrgv2o61htxgoqh3/1tbiNRegYWp3DJevVgAA3c 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 --- 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