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=-10.1 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,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 00CEEC2D0EE for ; Fri, 27 Mar 2020 22:25:11 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 25BD92173E for ; Fri, 27 Mar 2020 22:25:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585347910; bh=z0cDMWPHjda8S1DQ/YXhUKhufGNi2+4CB+bAP+nrCxg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=H5TTZW5BI1wWYBHfjgkZtjHd4bYYpqYvhqO8o4VVJomweIFuGxGfYEH+pcMPA1x1x ui1JQ8SAkjiTpIWbrfBPokWlk6A1vl44f5ieDoaWHpDV3TOH9Ay45crOlbVzD69Hdt 2vQIEp0bitCLu8vAlBsXtNcIi3B1v95+/kqtuxgg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727883AbgC0WZJ (ORCPT ); Fri, 27 Mar 2020 18:25:09 -0400 Received: from mail.kernel.org ([198.145.29.99]:43282 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727860AbgC0WZJ (ORCPT ); Fri, 27 Mar 2020 18:25:09 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (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 A17AC21655; Fri, 27 Mar 2020 22:25:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585347906; bh=z0cDMWPHjda8S1DQ/YXhUKhufGNi2+4CB+bAP+nrCxg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Y9RiKNwpLGjZX4S+C4uJ2yOq5NrLQJa126vyZ8+yYfVwuOIcUMUdCdRRc2wSLkZUK uWB4i16ak+OUOSl3s4tZA4PSBImE2rF5+BxGGo+C/8Egjm4us3hEJcBbQIJM8LN390 bFPh7JmqXdt0TPoOKlxZcioeTtg0NOP4LZ+MngXo= 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, dipankar@in.ibm.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" Subject: [PATCH v3 tip/core/rcu 25/34] rcu-tasks: Add Kconfig option to mediate smp_mb() vs. IPI Date: Fri, 27 Mar 2020 15:24:47 -0700 Message-Id: <20200327222456.12470-25-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200327222346.GA12082@paulmck-ThinkPad-P72> References: <20200327222346.GA12082@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" This commit provides a new TASKS_TRACE_RCU_READ_MB Kconfig option that enables use of read-side memory barriers by both rcu_read_lock_trace() and rcu_read_unlock_trace() when the are executed with the current->trc_reader_special.b.need_mb flag set. This flag is currently never set. Doing that is the subject of a later commit. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_trace.h | 3 ++- kernel/rcu/Kconfig | 18 ++++++++++++++++++ kernel/rcu/tasks.h | 3 ++- 3 files changed, 22 insertions(+), 2 deletions(-) diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h index c42b365c..4c25a41 100644 --- a/include/linux/rcupdate_trace.h +++ b/include/linux/rcupdate_trace.h @@ -50,7 +50,8 @@ static inline void rcu_read_lock_trace(void) struct task_struct *t = current; WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); - if (t->trc_reader_special.b.need_mb) + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && + t->trc_reader_special.b.need_mb) smp_mb(); // Pairs with update-side barriers rcu_lock_acquire(&rcu_trace_lock_map); } diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig index cb1d18e..0ebe15a 100644 --- a/kernel/rcu/Kconfig +++ b/kernel/rcu/Kconfig @@ -234,4 +234,22 @@ config RCU_NOCB_CPU Say Y here if you want to help to debug reduced OS jitter. Say N here if you are unsure. +config TASKS_TRACE_RCU_READ_MB + bool "Tasks Trace RCU readers use memory barriers in user and idle" + depends on RCU_EXPERT + default PREEMPT_RT || NR_CPUS < 8 + help + Use this option to further reduce the number of IPIs sent + to CPUs executing in userspace or idle during tasks trace + RCU grace periods. Given that a reasonable setting of + the rcupdate.rcu_task_ipi_delay kernel boot parameter + eliminates such IPIs for many workloads, proper setting + of this Kconfig option is important mostly for aggressive + real-time installations and for battery-powered devices, + hence the default chosen above. + + Say Y here if you hate IPIs. + Say N here if you hate read-side memory barriers. + Take the default if you are unsure. + endmenu # "RCU Subsystem" diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index f9a828c..b18298b 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -734,7 +734,8 @@ void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) { int nq = t->trc_reader_special.b.need_qs; - if (t->trc_reader_special.b.need_mb) + if (IS_ENABLED(CONFIG_TASKS_TRACE_RCU_READ_MB) && + t->trc_reader_special.b.need_mb) smp_mb(); // Pairs with update-side barriers. // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. if (nq) -- 2.9.5