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=-13.1 required=3.0 tests=BAYES_00,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_GIT 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 2BBA2C388F7 for ; Thu, 5 Nov 2020 23:01:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DC75D2071A for ; Thu, 5 Nov 2020 23:01:30 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617290; bh=fz2HhQJRCVuQiOPMD551kUBRgNfqMQdtpKHjhwrMEso=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=yc5YFuTKbnffHU579C4Pe7zThCTKqWJ7uf62ZHlftJ9VRxn9RXG3qgDZ+dCO2lCFi VOp5HfiToY3rozP5a6iFEy3mSS5lD2W24C42DyPq0C9krKUwJ/5PMGCmhNizcokH0s kIFUxy59BuIm20IrlXanAaSj3tWqi8GuATZ196G8= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732518AbgKEXB3 (ORCPT ); Thu, 5 Nov 2020 18:01:29 -0500 Received: from mail.kernel.org ([198.145.29.99]:59014 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1731899AbgKEXB3 (ORCPT ); Thu, 5 Nov 2020 18:01:29 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D4CA620782; Thu, 5 Nov 2020 23:01:27 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1604617288; bh=fz2HhQJRCVuQiOPMD551kUBRgNfqMQdtpKHjhwrMEso=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Cqjgu4QBg/SzXVn2KlMlYh14uJDIUF9J7GH/aAYdAwP0U+t97tkD5nliDDWe8ICRt nCNAmogqpthy78hb7waUDeRfsq4HiYgC0z4U8vlI8o++s5dSB+a9/moESCCGTZnao2 awGNKG8R0+P8dunSTykc+19y9WLGNHDQUW1v9YIo= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" , "Rafael J . Wysocki" , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org Subject: [PATCH tip/core/rcu 2/2] x86/cpu: Avoid cpuinfo-induced IPIing of idle CPUs Date: Thu, 5 Nov 2020 15:01:23 -0800 Message-Id: <20201105230123.18308-2-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20201105230040.GA18202@paulmck-ThinkPad-P72> References: <20201105230040.GA18202@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" Currently, accessing /proc/cpuinfo sends IPIs to idle CPUs in order to learn their clock frequency. Which is a bit strange, given that waking them from idle likely significantly changes their clock frequency. This commit therefore avoids sending /proc/cpuinfo-induced IPIs to idle CPUs. [ paulmck: Also check for idle in arch_freq_prepare_all(). ] Signed-off-by: Paul E. McKenney Cc: Rafael J. Wysocki Cc: Thomas Gleixner Cc: Ingo Molnar Cc: Borislav Petkov Cc: "H. Peter Anvin" Cc: --- arch/x86/kernel/cpu/aperfmperf.c | 6 ++++++ include/linux/rcutiny.h | 2 ++ include/linux/rcutree.h | 1 + kernel/rcu/tree.c | 8 ++++++++ 4 files changed, 17 insertions(+) diff --git a/arch/x86/kernel/cpu/aperfmperf.c b/arch/x86/kernel/cpu/aperfmperf.c index 37ff7f4..47af9b7 100644 --- a/arch/x86/kernel/cpu/aperfmperf.c +++ b/arch/x86/kernel/cpu/aperfmperf.c @@ -14,6 +14,7 @@ #include #include #include +#include #include "cpu.h" @@ -93,6 +94,9 @@ unsigned int aperfmperf_get_khz(int cpu) if (!housekeeping_cpu(cpu, HK_FLAG_MISC)) return 0; + if (rcu_is_idle_cpu(cpu)) + return 0; /* Idle CPUs are completely uninteresting. */ + aperfmperf_snapshot_cpu(cpu, ktime_get(), true); return per_cpu(samples.khz, cpu); } @@ -112,6 +116,8 @@ void arch_freq_prepare_all(void) for_each_online_cpu(cpu) { if (!housekeeping_cpu(cpu, HK_FLAG_MISC)) continue; + if (rcu_is_idle_cpu(cpu)) + continue; /* Idle CPUs are completely uninteresting. */ if (!aperfmperf_snapshot_cpu(cpu, now, false)) wait = true; } diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h index 7c1ecdb..2a97334 100644 --- a/include/linux/rcutiny.h +++ b/include/linux/rcutiny.h @@ -89,6 +89,8 @@ static inline void rcu_irq_enter_irqson(void) { } static inline void rcu_irq_exit(void) { } static inline void rcu_irq_exit_preempt(void) { } static inline void rcu_irq_exit_check_preempt(void) { } +#define rcu_is_idle_cpu(cpu) \ + (is_idle_task(current) && !in_nmi() && !in_irq() && !in_serving_softirq()) static inline void exit_rcu(void) { } static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t) { diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h index 59eb5cd..df578b7 100644 --- a/include/linux/rcutree.h +++ b/include/linux/rcutree.h @@ -50,6 +50,7 @@ void rcu_irq_exit(void); void rcu_irq_exit_preempt(void); void rcu_irq_enter_irqson(void); void rcu_irq_exit_irqson(void); +bool rcu_is_idle_cpu(int cpu); #ifdef CONFIG_PROVE_RCU void rcu_irq_exit_check_preempt(void); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 06895ef..1d84c0b 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -341,6 +341,14 @@ static bool rcu_dynticks_in_eqs(int snap) return !(snap & RCU_DYNTICK_CTRL_CTR); } +/* Return true if the specified CPU is currently idle from an RCU viewpoint. */ +bool rcu_is_idle_cpu(int cpu) +{ + struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); + + return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)); +} + /* * Return true if the CPU corresponding to the specified rcu_data * structure has spent some time in an extended quiescent state since -- 2.9.5