From nobody Mon Feb 9 20:30:31 2026 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 A2F0241AAC for ; Wed, 30 Apr 2025 01:05:27 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745975127; cv=none; b=cpASn1Qe3/cMOC05fR4/QEhpZWII9CO7r1fNG3CO94o2u4KuGmfvzDLIcH69CrA+votal7vEtNinBPeILYaU3Xb5NBzmb/pTwrtfG4MNigW5G1Gxz4pdFpttMgW+/AeDPAEDAYwN18aWumGEjChv+K5XluLJ8Zg/dGD6I5SHMBw= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745975127; c=relaxed/simple; bh=NCii0AygsQ7t/hzmWNQsffMOxKXMFGYLlumd3Gn7O9s=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=lpmF6Uuqr/c1Nk00frBKN4LYBx2V/2IAhovjAQT//LOhMm+WPIDUli/fIyZJniXLCJ1ggkXAhB4GNHrgD1RMASB6pr67QRkNuLYgGR2P25sfa521nG2At4ss8JiwWa0X7K2uVAcSy9HH30HY8oB4CAbeDW4S/N0m1KzCXWhrdqg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=q27b/DA2; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="q27b/DA2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D876C4CEF2; Wed, 30 Apr 2025 01:05:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745975127; bh=NCii0AygsQ7t/hzmWNQsffMOxKXMFGYLlumd3Gn7O9s=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=q27b/DA2L68ZFp80NHX0Cpuf7QxNXmW6PXrwrGwXEdQ4pReA+bU2TTG9GH4gRtCS3 lozfkTEW+zrY6C4oyPDbsxU5+5khX7JRt85tODrQBP5SXyv17vO7P/jGmrSNWcKzFK Xw2+g1qsnssvOy7RAaD5kQAvJhlck3l41K5TxogSPUI+NwBsaTh+1pRlucmMxLShik dBmMYRQwVuypD4+oun+TswTyHxz6VAnxC9deMUBrxeCK6UWLkp6NIV6M70uMZA7OVf zcSF7zs/aS4BSGKft9O2XvyV1U0l/5H51w1WeLjzxlb5HGd0ILKCUbf5+s/xdh3Qo2 lCSMl1v+SoTqQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id CE475CE112C; Tue, 29 Apr 2025 18:05:25 -0700 (PDT) From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: kernel-team@meta.com, Andrew Morton , Kuniyuki Iwashima , Mateusz Guzik , Petr Mladek , Steven Rostedt , John Ogness , Sergey Senozhatsky , Jon Pan-Doh , Bjorn Helgaas , Karolina Stolarek , "Paul E. McKenney" Subject: [PATCH v4 14/20] ratelimit: Avoid atomic decrement under lock if already rate-limited Date: Tue, 29 Apr 2025 18:05:18 -0700 Message-Id: <20250430010524.3614408-14-paulmck@kernel.org> X-Mailer: git-send-email 2.40.1 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Currently, if the lock is acquired, the code unconditionally does an atomic decrement on ->rs_n_left, even if that atomic operation is guaranteed to return a limit-rate verdict. A limit-rate verdict will in fact be the common case when something is spewing into a rate limit. This unconditional atomic operation incurs needless overhead and also raises the spectre of counter wrap. Therefore, do the atomic decrement only if there is some chance that rates won't be limited. Link: https://lore.kernel.org/all/fbe93a52-365e-47fe-93a4-44a44547d601@paul= mck-laptop/ Link: https://lore.kernel.org/all/20250423115409.3425-1-spasswolf@web.de/ Signed-off-by: Paul E. McKenney Reviewed-by: Petr Mladek Cc: Andrew Morton Cc: Kuniyuki Iwashima Cc: Mateusz Guzik Cc: Steven Rostedt Cc: John Ogness Cc: Sergey Senozhatsky --- lib/ratelimit.c | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/lib/ratelimit.c b/lib/ratelimit.c index a7aaebb7a7189..ab8472edeb1d2 100644 --- a/lib/ratelimit.c +++ b/lib/ratelimit.c @@ -103,13 +103,16 @@ int ___ratelimit(struct ratelimit_state *rs, const ch= ar *func) } } if (burst) { - int n_left; + int n_left =3D atomic_read(&rs->rs_n_left); =20 /* The burst might have been taken by a parallel call. */ - n_left =3D atomic_dec_return(&rs->rs_n_left); - if (n_left >=3D 0) { - ret =3D 1; - goto unlock_ret; + + if (n_left > 0) { + n_left =3D atomic_dec_return(&rs->rs_n_left); + if (n_left >=3D 0) { + ret =3D 1; + goto unlock_ret; + } } } =20 --=20 2.40.1