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=-8.8 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 2F0ABC433E0 for ; Wed, 13 May 2020 23:03:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3170C20693 for ; Wed, 13 May 2020 23:03:36 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589411016; bh=JiwzGxwWx0NS2EXPzf/2f+eKgUV2OMKFWgrmHm0qu7Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=udWCKKm/Tbh/FvCMO9cVq2+rWRaejobCzzXRpFmAdjGFQE/H4SvikMaGLAnhKO0pl Ftn/b+4J11+90t6eRisaul74h3/2qpXPlFnqORBuWrZ4MYjptjEbh1Dw6XmvnDafjw /KPFiq9cfi4/6Kp6He96CeFzSDjhLzierIinkVP0= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732235AbgEMXDf (ORCPT ); Wed, 13 May 2020 19:03:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:39166 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731815AbgEMXDe (ORCPT ); Wed, 13 May 2020 19:03:34 -0400 Received: from localhost (lfbn-ncy-1-985-231.w90-101.abo.wanadoo.fr [90.101.63.231]) (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 68FA020675; Wed, 13 May 2020 23:03:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1589411013; bh=JiwzGxwWx0NS2EXPzf/2f+eKgUV2OMKFWgrmHm0qu7Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pfBmySLrlBzf6/zjgOQhFegBu6eehkX+0kWEeQvRtOIhqFr49C8qBjJJ9+muojnjn Eq/KnmMeYaP31Symr8RsvMxXPTEArPnnd2/Vx3ljZBxsTmpzCS1fqHzwEFHv8+852R q1w9FgWfeY2/0ZaP6wOP/AD4NcTG2ZStFHsgO+wY= Date: Thu, 14 May 2020 01:03:31 +0200 From: Frederic Weisbecker To: "Paul E. McKenney" 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: <20200513230330.GB18303@lenoir> References: <20200513164714.22557-1-frederic@kernel.org> <20200513164714.22557-5-frederic@kernel.org> <20200513182029.GT2869@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200513182029.GT2869@paulmck-ThinkPad-P72> 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 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 ? > > > /* > > * 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 ;-)