From mboxrd@z Thu Jan 1 00:00:00 1970 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 2C5E8263F34; Mon, 19 Jan 2026 23:53:30 +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=1768866811; cv=none; b=dv/0XjybNhi9Ea/jMJ1ssrLgxAb010PYQHxSAYtlM6Mz+z2ZYXobLMATarUgtGrDHErboK9lLdLXbEIbv+Fyv6JzCt4caSypOdNzS4DHHnKyhApheNLQDhoEwfREBkg2e36K28JiJxXFskaXf6rpH5n/8ntrSvMu4JgFGaN6q7M= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768866811; c=relaxed/simple; bh=U/T6evyeL/QW1UF3DGDmeiZ7ztFTZk1lfnv2Gys3oTU=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=dSF+9X2LWGDsRj9hRJDUxf68+/QbkEozHdrq3L6aajXI7n+9ohxOlA6UfbDLVNq/Gy9DrgcZyvIFXUJWUUrJr3LaeaO/L2TQFtlOfLbkqIJsRW7fh4jJRCM0Hug0n8XnBtl4FR0NaKX0TGjLxH86/TFqp5y5ol3rBBsFc7Qmf44= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=FDMMhyFu; 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="FDMMhyFu" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F1746C116C6; Mon, 19 Jan 2026 23:53:29 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768866810; bh=U/T6evyeL/QW1UF3DGDmeiZ7ztFTZk1lfnv2Gys3oTU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=FDMMhyFueakSc30fH0avs93RU8BIuTjLP9Jw9Zacu2tlsCAJVu/C6T5pVyRTSDLmf kFCqu+Ujop6ah+Jz+5Ipl4ojvu+eNw0tWehYODIyAI+DTJ0gf8BiFS/+H5yN1S7D0E puCtBY2ca49Y35ZqVUN/Jzi5tIAoST0z/e0N9wObpvewOt0bt52HZGDNPUlfCV7IST clcaRE89XbN3N5R1rdt1nnUoioFjDWecAVzWDbCJP9lMU4cju81UwH7+7mdrh6j6t+ lKjHoRuJM+OAeHuwtD8fGeETn8CdzZ1YtwgC+EzkK8I7yGFkXGeQFh8MTeIZ5A4RGz 7yk72yR4Mmrqw== Date: Tue, 20 Jan 2026 00:53:26 +0100 From: Frederic Weisbecker To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, "Paul E . McKenney" , Boqun Feng , rcu@vger.kernel.org, Neeraj Upadhyay , Josh Triplett , Uladzislau Rezki , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Zqiang Subject: Re: [PATCH -next v3 2/3] rcu/nocb: Remove dead callback overload handling Message-ID: References: <20260119231223.989409-1-joelagnelf@nvidia.com> <20260119231223.989409-3-joelagnelf@nvidia.com> Precedence: bulk X-Mailing-List: rcu@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260119231223.989409-3-joelagnelf@nvidia.com> Le Mon, Jan 19, 2026 at 06:12:22PM -0500, Joel Fernandes a écrit : > During callback overload (exceeding qhimark), the NOCB code attempts > opportunistic advancement via rcu_advance_cbs_nowake(). Analysis shows > this entire code path is dead: > > - 30 overload conditions triggered with 300,000 callback flood > - 0 advancements actually occurred > - 100% of time blocked because current GP not done > > The overload condition triggers when callbacks are coming in at a high > rate with GPs not completing as fast. But the advancement requires the > GP to be complete - a logical contradiction. Even if the GP did complete > in time, nocb_gp_wait() has to wake up anyway to do the advancement, so > it is pointless. > > Since the advancement is dead code, the entire overload handling block > serves no purpose. Remove it entirely. > > Suggested-by: Frederic Weisbecker > Signed-off-by: Joel Fernandes Reviewed-by: Frederic Weisbecker Would be nice to have Paul's ack as well, in case we missed something subtle here. Also probably for upcoming merge window + 1, note that similar code with similar removal opportunity resides in rcu_nocb_try_bypass(). And ->nocb_gp_adv_time could then be removed. Thanks. -- Frederic Weisbecker SUSE Labs