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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 173A9C63797 for ; Thu, 12 Jan 2023 23:50:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235124AbjALXuT (ORCPT ); Thu, 12 Jan 2023 18:50:19 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49328 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232888AbjALXuR (ORCPT ); Thu, 12 Jan 2023 18:50:17 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 33FDDA45F; Thu, 12 Jan 2023 15:50:16 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id D6A08B82039; Thu, 12 Jan 2023 23:50:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 672B7C433D2; Thu, 12 Jan 2023 23:50:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1673567413; bh=N4m4bXPk4Vvg4JUzPHaMx6XKiDu3zzjCCgl7Rx7jJqI=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=soxLYVYVJmOnxATKSgIyibxbYO9gKNhpTnPVSRBc1/Y8o88BewcvkLzq9X0KLQlwc Soi6IWDb6ABGMGT7ghTTb51jJc38e5oAJS3tHECGFor9LDUD6FUtw14RQ2qayCVbme PXcPKfEgr7xicG/BcdFb4AHo59U4YNQaYv+aLrVm7BZ0c0O8F5uyRVpi3eDZtwJBS/ bhW1NIVkKrUeDLAUHGA/Ys3vVVmy3FRjwfCpJSVHY8G+j1CExT8oBVq5laomlh4tDR 5WwiF5QbxL2ZJ6fUxQDs752Q06U5v/1T4nkl5YzaXR/kVVLzKUhN5Pzb15hLyjDh7i Ja1vUdLUQdBOA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 066C45C09F1; Thu, 12 Jan 2023 15:50:13 -0800 (PST) Date: Thu, 12 Jan 2023 15:50:13 -0800 From: "Paul E. McKenney" To: Joel Fernandes Cc: linux-kernel@vger.kernel.org, Josh Triplett , Lai Jiangshan , Mathieu Desnoyers , rcu@vger.kernel.org, Steven Rostedt , fweisbec@gmail.com, urezki@gmail.com Subject: Re: [PATCH v2 rcu/dev 1/2] rcu: Track laziness during boot and suspend Message-ID: <20230112235013.GU4028633@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20230112192724.GA3610129@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 12, 2023 at 05:25:51PM -0500, Joel Fernandes wrote: > > > > On Jan 12, 2023, at 2:27 PM, Paul E. McKenney wrote: > > > > On Thu, Jan 12, 2023 at 12:52:22AM +0000, Joel Fernandes (Google) wrote: > >> During boot and suspend/resume, it is desired to prevent RCU laziness from > >> effecting performance and in some cases failures like with suspend. > >> > >> Track whether RCU laziness is to be ignored or not, in kernels with > >> CONFIG_RCU_LAZY enabled. We do such tracking for expedited-RCU already, however > >> since Android currently expedites synchronous_rcu() always, we cannot rely on > >> that. The next patch ignores laziness hints based on this tracking. > >> > >> Signed-off-by: Joel Fernandes (Google) > >> --- > >> Paul, could we take this and the next one for 6.2 -rc cycle? > >> > >> I also booted debian Linux and verified the flag is reset correctly after boot > >> completes. Thanks. > > > > After going back and forth a bit, I took these two as-is (aside from > > the usual commit-log wordsmithing). > > > > At some point, the state-change-notification from things like boot, > > suspend/resume, sysrq-t, and panic() should probably be refactored. > > But I do not believe that we are yet at that point, and there is not > > much point in half-refactorings in cases such as this one. > > > > I added the Fixes tags, and, if testing goes well, I plan to submit > > them into the upcoming merge window. I have no reason to believe that > > anyone is hitting this, it is only a few weeks away anyhow, and a good > > chunk of that would be consumed by testing and review. > > > > And if someone does hit it, we do have your fixes to send to them, so > > thank you for that! > > (These won't become visible on -rcu until I complete today's rebase, > > in case you were wondering.) > > Thanks and this sounds good to me. Meanwhile I pulled into our product kernel so all is good. Very good! Please let me know how it goes! Thanx, Paul > Thanks, > > - Joel > > > > > > Thanx, Paul > > > >> kernel/rcu/rcu.h | 6 ++++++ > >> kernel/rcu/tree.c | 2 ++ > >> kernel/rcu/update.c | 40 +++++++++++++++++++++++++++++++++++++++- > >> 5 files changed, 55 insertions(+), 1 deletion(-) > >> create mode 100644 cc_list > >> create mode 100644 to_list > >> > >> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h > >> index 5c8013f7085f..115616ac3bfa 100644 > >> --- a/kernel/rcu/rcu.h > >> +++ b/kernel/rcu/rcu.h > >> @@ -449,14 +449,20 @@ do { \ > >> /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */ > >> static inline bool rcu_gp_is_normal(void) { return true; } > >> static inline bool rcu_gp_is_expedited(void) { return false; } > >> +static inline bool rcu_async_should_hurry(void) { return false; } > >> static inline void rcu_expedite_gp(void) { } > >> static inline void rcu_unexpedite_gp(void) { } > >> +static inline void rcu_async_hurry(void) { } > >> +static inline void rcu_async_relax(void) { } > >> static inline void rcu_request_urgent_qs_task(struct task_struct *t) { } > >> #else /* #ifdef CONFIG_TINY_RCU */ > >> bool rcu_gp_is_normal(void); /* Internal RCU use. */ > >> bool rcu_gp_is_expedited(void); /* Internal RCU use. */ > >> +bool rcu_async_should_hurry(void); /* Internal RCU use. */ > >> void rcu_expedite_gp(void); > >> void rcu_unexpedite_gp(void); > >> +void rcu_async_hurry(void); > >> +void rcu_async_relax(void); > >> void rcupdate_announce_bootup_oddness(void); > >> #ifdef CONFIG_TASKS_RCU_GENERIC > >> void show_rcu_tasks_gp_kthreads(void); > >> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > >> index 63545d79da51..78b2e999c904 100644 > >> --- a/kernel/rcu/tree.c > >> +++ b/kernel/rcu/tree.c > >> @@ -4504,11 +4504,13 @@ static int rcu_pm_notify(struct notifier_block *self, > >> switch (action) { > >> case PM_HIBERNATION_PREPARE: > >> case PM_SUSPEND_PREPARE: > >> + rcu_async_hurry(); > >> rcu_expedite_gp(); > >> break; > >> case PM_POST_HIBERNATION: > >> case PM_POST_SUSPEND: > >> rcu_unexpedite_gp(); > >> + rcu_async_relax(); > >> break; > >> default: > >> break; > >> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c > >> index 3893022f8ed8..19bf6fa3ee6a 100644 > >> --- a/kernel/rcu/update.c > >> +++ b/kernel/rcu/update.c > >> @@ -144,8 +144,45 @@ bool rcu_gp_is_normal(void) > >> } > >> EXPORT_SYMBOL_GPL(rcu_gp_is_normal); > >> > >> -static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); > >> +static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1); > >> +/* > >> + * Should call_rcu() callbacks be processed with urgency or are > >> + * they OK being executed with arbitrary delays? > >> + */ > >> +bool rcu_async_should_hurry(void) > >> +{ > >> + return !IS_ENABLED(CONFIG_RCU_LAZY) || > >> + atomic_read(&rcu_async_hurry_nesting); > >> +} > >> +EXPORT_SYMBOL_GPL(rcu_async_should_hurry); > >> + > >> +/** > >> + * rcu_async_hurry - Make future async RCU callbacks not lazy. > >> + * > >> + * After a call to this function, future calls to call_rcu() > >> + * will be processed in a timely fashion. > >> + */ > >> +void rcu_async_hurry(void) > >> +{ > >> + if (IS_ENABLED(CONFIG_RCU_LAZY)) > >> + atomic_inc(&rcu_async_hurry_nesting); > >> +} > >> +EXPORT_SYMBOL_GPL(rcu_async_hurry); > >> > >> +/** > >> + * rcu_async_relax - Make future async RCU callbacks lazy. > >> + * > >> + * After a call to this function, future calls to call_rcu() > >> + * will be processed in a lazy fashion. > >> + */ > >> +void rcu_async_relax(void) > >> +{ > >> + if (IS_ENABLED(CONFIG_RCU_LAZY)) > >> + atomic_dec(&rcu_async_hurry_nesting); > >> +} > >> +EXPORT_SYMBOL_GPL(rcu_async_relax); > >> + > >> +static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1); > >> /* > >> * Should normal grace-period primitives be expedited? Intended for > >> * use within RCU. Note that this function takes the rcu_expedited > >> @@ -195,6 +232,7 @@ static bool rcu_boot_ended __read_mostly; > >> void rcu_end_inkernel_boot(void) > >> { > >> rcu_unexpedite_gp(); > >> + rcu_async_relax(); > >> if (rcu_normal_after_boot) > >> WRITE_ONCE(rcu_normal, 1); > >> rcu_boot_ended = true; > >> -- > >> 2.39.0.314.g84b9a713c41-goog