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 BCFEE1B3931; Fri, 13 Dec 2024 23:08:45 +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=1734131325; cv=none; b=UE6okEYheRY4Vss92YISzg2BvZyxL12KyE888rsTGghsqXPLUzd1RqKRGysrpjdfjFBVBHfw7TV8LlfSTqZpDTSJ1T1gPSkO3rJKKddkVWsOMrdn627cagw1hxeV9OJ0IXQlvvn8TPgUfB58n3ozN5XWcv6iLvvajrtFOqPRQ4c= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1734131325; c=relaxed/simple; bh=6+cPR9eBHLpkUUg7WipONtqTType85yW8E6MJO2HpOY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QGDFdbD6bek8obL/itPCPi9VFk7uXTJjSNmDJ4Hq7nZPg1U2XGPo8rWWpE+LtbszMSShgZwWJySBorVsRIRLCXsNxv3zgNJybLxQeAYq0CiFNSXJlm4YMB7U20c0wMohxIee0Szecmcmvzlbb6LrxDFaLUsslDbrWdQWFmtvbus= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=DpZgD7D2; 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="DpZgD7D2" Received: by smtp.kernel.org (Postfix) with ESMTPSA id DE1FAC4CED4; Fri, 13 Dec 2024 23:08:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1734131325; bh=6+cPR9eBHLpkUUg7WipONtqTType85yW8E6MJO2HpOY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=DpZgD7D2mVEFuc54tXaH8qGjEi+05SpRQwBX6Y0ZYHUBnu7lE3QVItquOwB2wYE2e SlbEQtaLjS2X5EkyQPCIvqIbZLn78SNWpWNZMb0hUfJEgzbMxGPOYRjKexIEFrtLut F+gW0lVOM5AE3+JVAYJEGl3lKZctAVlRQTnBQg0rxsrkzE4FnTROLRX4XZ2t+YuPlF WPTfZdfirqAjxcI4Jjcg2AHYkz/7oEfqBR7qKfcbjALlUESvsv9I39vOviULuyAuRX YsrN0znWm+evs6C4F9BOLiR6e53c8iR4Ikx+CbkR3BXhqjZhHj+UJ8ttMNGmcgt16e 1oldTzyNIybwA== Date: Sat, 14 Dec 2024 00:08:42 +0100 From: Frederic Weisbecker To: "Paul E. McKenney" Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org Subject: Re: [PATCH rcu 1/2] rcu/nocb: Use switch/case on NOCB timer state machine Message-ID: References: <20241212184214.2018411-1-paulmck@kernel.org> 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: <20241212184214.2018411-1-paulmck@kernel.org> Le Thu, Dec 12, 2024 at 10:42:13AM -0800, Paul E. McKenney a écrit : > From: Frederic Weisbecker > > It's more convenient to benefit from the fallthrough feature of > switch / case to handle the timer state machine. Also a new state is > about to be added that will take advantage of it. > > No intended functional change. > > Signed-off-by: Frederic Weisbecker > Signed-off-by: Paul E. McKenney Please drop this one too. It introduced a subtle (yet desired) behaviour change as Boqun noted. I'll resend a better version. Thanks! > --- > kernel/rcu/tree_nocb.h | 33 +++++++++++++++++++++++---------- > 1 file changed, 23 insertions(+), 10 deletions(-) > > diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h > index 2605dd234a13c..0923d60c5a338 100644 > --- a/kernel/rcu/tree_nocb.h > +++ b/kernel/rcu/tree_nocb.h > @@ -271,22 +271,35 @@ static void wake_nocb_gp_defer(struct rcu_data *rdp, int waketype, > > raw_spin_lock_irqsave(&rdp_gp->nocb_gp_lock, flags); > > - /* > - * Bypass wakeup overrides previous deferments. In case of > - * callback storms, no need to wake up too early. > - */ > - if (waketype == RCU_NOCB_WAKE_LAZY && > - rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) { > - mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush()); > - WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); > - } else if (waketype == RCU_NOCB_WAKE_BYPASS) { > + switch (waketype) { > + case RCU_NOCB_WAKE_BYPASS: > + /* > + * Bypass wakeup overrides previous deferments. In case of > + * callback storms, no need to wake up too early. > + */ > mod_timer(&rdp_gp->nocb_timer, jiffies + 2); > WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); > - } else { > + break; > + case RCU_NOCB_WAKE_LAZY: > + if (rdp->nocb_defer_wakeup == RCU_NOCB_WAKE_NOT) { > + mod_timer(&rdp_gp->nocb_timer, jiffies + rcu_get_jiffies_lazy_flush()); > + WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); > + } > + /* > + * If the timer is already armed, a non-lazy enqueue may have happened > + * in-between. Don't delay it and fall-through. > + */ > + break; > + case RCU_NOCB_WAKE: > + fallthrough; > + case RCU_NOCB_WAKE_FORCE: > if (rdp_gp->nocb_defer_wakeup < RCU_NOCB_WAKE) > mod_timer(&rdp_gp->nocb_timer, jiffies + 1); > if (rdp_gp->nocb_defer_wakeup < waketype) > WRITE_ONCE(rdp_gp->nocb_defer_wakeup, waketype); > + break; > + default: > + WARN_ON_ONCE(1); > } > > raw_spin_unlock_irqrestore(&rdp_gp->nocb_gp_lock, flags); > -- > 2.40.1 >