From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5822EC433E0 for ; Thu, 14 May 2020 15:47:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 20FEB2065D for ; Thu, 14 May 2020 15:47:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589471277; bh=x6s1E+XROP/HiuUxOMycOoCvxjDKnPS1UbGWfOMKnCA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=OKb48BWsH6kgFruoy6sFKaxfIHNqIn+1ORKEuI96/gAO5o7QbRZvdzaJja+tOHZZ9 XqBMwfYpPbzJ1S8Sd+K2P9p50K/poAdpkgn0w2v5/i3XPFKdpHWVxSe5K8Ia5m4Y+j KT8ha0LwGUldfKrpE1tlKBbFqNMq6PutA6pLi7Pk= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727946AbgENPr4 (ORCPT ); Thu, 14 May 2020 11:47:56 -0400 Received: from mail.kernel.org ([198.145.29.99]:40872 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726140AbgENPrz (ORCPT ); Thu, 14 May 2020 11:47:55 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 1542420657; Thu, 14 May 2020 15:47:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589471275; bh=x6s1E+XROP/HiuUxOMycOoCvxjDKnPS1UbGWfOMKnCA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=b6Pi2ErAe9bOmJkaLrmAPcJV/MEsaEge68OojgxVidZNqp3v6d941ttkf9V/N+DnL 9mx2J0Ar/r5sW+TqTaJmPuJ20qDq7e3FFx1Mx/aiuydUxT/W3hK94xQVKAqWIkt4oz X8NV94wCAjwP+7P6W0IKQUcuHp0CaYpB2t4LNHFk= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id F1BF335229C5; Thu, 14 May 2020 08:47:54 -0700 (PDT) Date: Thu, 14 May 2020 08:47:54 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: LKML , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , Josh Triplett Subject: Re: [PATCH 04/10] rcu: Implement rcu_segcblist_is_offloaded() config dependent Message-ID: <20200514154754.GM2869@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200513164714.22557-1-frederic@kernel.org> <20200513164714.22557-5-frederic@kernel.org> <20200513182029.GT2869@paulmck-ThinkPad-P72> <20200513230330.GB18303@lenoir> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200513230330.GB18303@lenoir> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, May 14, 2020 at 01:03:31AM +0200, Frederic Weisbecker wrote: > On Wed, May 13, 2020 at 11:20:29AM -0700, Paul E. McKenney wrote: > > On Wed, May 13, 2020 at 06:47:08PM +0200, Frederic Weisbecker wrote: > > > This simplify the usage of this API and avoid checking the kernel > > > config from the callers. > > > > > > Signed-off-by: Frederic Weisbecker > > > Cc: Paul E. McKenney > > > Cc: Josh Triplett > > > Cc: Steven Rostedt > > > Cc: Mathieu Desnoyers > > > Cc: Lai Jiangshan > > > Cc: Joel Fernandes > > > --- > > > include/linux/rcu_segcblist.h | 2 ++ > > > kernel/rcu/rcu_segcblist.c | 2 ++ > > > kernel/rcu/rcu_segcblist.h | 6 ++++++ > > > kernel/rcu/tree.c | 21 +++++++-------------- > > > 4 files changed, 17 insertions(+), 14 deletions(-) > > > > > > diff --git a/include/linux/rcu_segcblist.h b/include/linux/rcu_segcblist.h > > > index b36afe7b22c9..0ced0a0ecbcf 100644 > > > --- a/include/linux/rcu_segcblist.h > > > +++ b/include/linux/rcu_segcblist.h > > > @@ -73,7 +73,9 @@ struct rcu_segcblist { > > > long len; > > > #endif > > > u8 enabled; > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > u8 offloaded; > > > +#endif > > > > Given that this is only one byte and that removing it won't actually > > save any memory on most architectures, why not just leave it and > > adjust as shown below? > > Right, the point was to make it private to that config and trigger > a build error otherwise. But if we have an off case that's fine. > > > > > > }; > > > > > > #define RCU_SEGCBLIST_INITIALIZER(n) \ > > > diff --git a/kernel/rcu/rcu_segcblist.c b/kernel/rcu/rcu_segcblist.c > > > index 9a0f66133b4b..d8ea2bef5574 100644 > > > --- a/kernel/rcu/rcu_segcblist.c > > > +++ b/kernel/rcu/rcu_segcblist.c > > > @@ -166,6 +166,7 @@ void rcu_segcblist_disable(struct rcu_segcblist *rsclp) > > > rsclp->enabled = 0; > > > } > > > > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > /* > > > * Mark the specified rcu_segcblist structure as offloaded. This > > > * structure must be empty. > > > @@ -174,6 +175,7 @@ void rcu_segcblist_offload(struct rcu_segcblist *rsclp) > > > { > > > rsclp->offloaded = 1; > > > } > > > +#endif > > > > Leave this unconditional, as it is nowhere near a fastpath. > > The point was to not raise false hopes to those who want to > offload when it's not supported. > > Let's perhaps have at least a WARN_ON_ONCE(1) if it is called > when !CONFIG_RCU_NOCB_CPU ? Sounds like a good choice to me! > > > /* > > > * Does the specified rcu_segcblist structure contain callbacks that > > > diff --git a/kernel/rcu/rcu_segcblist.h b/kernel/rcu/rcu_segcblist.h > > > index 5c293afc07b8..4c1503a82492 100644 > > > --- a/kernel/rcu/rcu_segcblist.h > > > +++ b/kernel/rcu/rcu_segcblist.h > > > @@ -62,7 +62,11 @@ static inline bool rcu_segcblist_is_enabled(struct rcu_segcblist *rsclp) > > > /* Is the specified rcu_segcblist offloaded? */ > > > static inline bool rcu_segcblist_is_offloaded(struct rcu_segcblist *rsclp) > > > { > > > +#ifdef CONFIG_RCU_NOCB_CPU > > > return rsclp->offloaded; > > > +#else > > > + return false; > > > +#endif > > > } > > > > Then this can just be: > > > > return IS_ENABLED(CONFIG_RCU_NOCB_CPU) && rsclp->offloaded; > > Ok. > > > > @@ -1401,8 +1401,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) > > > { > > > bool ret = false; > > > bool need_qs; > > > - const bool offloaded = IS_ENABLED(CONFIG_RCU_NOCB_CPU) && > > > - rcu_segcblist_is_offloaded(&rdp->cblist); > > > + const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); > > > > The adjustment to rcu_segcblist_is_offloaded() allows this (welcome!) > > simplification to remain. > > Ok thanks! > > > > @@ -3243,8 +3237,7 @@ static int rcu_pending(int user) > > > > > > /* Has RCU gone idle with this CPU needing another grace period? */ > > > if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && > > > - (!IS_ENABLED(CONFIG_RCU_NOCB_CPU) || > > > - !rcu_segcblist_is_offloaded(&rdp->cblist)) && > > > + !rcu_segcblist_is_offloaded(&rdp->cblist) && > > > > Ditto. > > > > As in "Why didn't I do it that way to start with???" ;-) > > You say that to someone who's too lazy to script short commands typed > 100 times a day ;-) ;-) ;-) ;-) Thanx, Paul