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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 701BEC43143 for ; Fri, 22 Jun 2018 06:12:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BDBE323DA6 for ; Fri, 22 Jun 2018 06:12:14 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BDBE323DA6 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lge.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751295AbeFVGMN (ORCPT ); Fri, 22 Jun 2018 02:12:13 -0400 Received: from lgeamrelo13.lge.com ([156.147.23.53]:39986 "EHLO lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1750931AbeFVGMM (ORCPT ); Fri, 22 Jun 2018 02:12:12 -0400 Received: from unknown (HELO lgeamrelo01.lge.com) (156.147.1.125) by 156.147.23.53 with ESMTP; 22 Jun 2018 15:12:09 +0900 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com Received: from unknown (HELO localhost.localdomain) (10.177.222.33) by 156.147.1.125 with ESMTP; 22 Jun 2018 15:12:09 +0900 X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com From: Byungchul Park To: jiangshanlai@gmail.com, paulmck@linux.vnet.ibm.com, josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com Cc: linux-kernel@vger.kernel.org, kernel-team@lge.com, joel@joelfernandes.org Subject: [PATCH] rcu: Refactor rcu_{nmi,irq}_{enter,exit}() Date: Fri, 22 Jun 2018 15:12:06 +0900 Message-Id: <1529647926-24427-1-git-send-email-byungchul.park@lge.com> X-Mailer: git-send-email 1.9.1 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When passing through irq or NMI contexts, the current code uses ->dynticks_nmi_nesting to detect if it's in the ourmost at the moment. Here, the thing is that all the related functions, rcu_irq_enter(), rcu_nmi_enter(), rcu_irq_exit() and rcu_nmi_exit() are carrying out the check within each under the following call relationship so there must be redundant conditional branches: rcu_irq_enter() /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() /* A conditional branch with ->dynticks_nmi_nesting */ /* A conditional branch with ->dynticks_nmi_nesting */ rcu_irq_exit() /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_exit() /* A conditional branch with ->dynticks_nmi_nesting */ /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_exit() /* A conditional branch with ->dynticks_nmi_nesting */ In order to make the code more readable and remove redundant conditional branches, we need to refactor rcu_{nmi,irq}_{enter,exit}() so they use a common function for each like: rcu_irq_enter() inlining rcu_nmi_enter_common(irq) /* A conditional branch with ->dynticks_nmi_nesting */ rcu_irq_exit() inlining rcu_nmi_exit_common(irq) /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_enter() inlining rcu_nmi_enter_common(nmi) /* A conditional branch with ->dynticks_nmi_nesting */ rcu_nmi_exit() inlining rcu_nmi_exit_common(nmi) /* A conditional branch with ->dynticks_nmi_nesting */ Suggested-by: Paul E. McKenney Signed-off-by: Byungchul Park --- kernel/rcu/tree.c | 59 ++++++++++++++++++++++++++++++++++++------------------- 1 file changed, 39 insertions(+), 20 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index deb2508..cdae85f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -764,17 +764,17 @@ void rcu_user_enter(void) #endif /* CONFIG_NO_HZ_FULL */ /** - * rcu_nmi_exit - inform RCU of exit from NMI context + * rcu_nmi_exit_common - inform RCU of exit from NMI context * * If we are returning from the outermost NMI handler that interrupted an * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting * to let the RCU grace-period handling know that the CPU is back to * being RCU-idle. * - * If you add or remove a call to rcu_nmi_exit(), be sure to test + * If you add or remove a call to rcu_nmi_exit_common(), be sure to test * with CONFIG_RCU_EQS_DEBUG=y. */ -void rcu_nmi_exit(void) +static __always_inline void rcu_nmi_exit_common(bool irq) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); @@ -800,7 +800,22 @@ void rcu_nmi_exit(void) /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks); WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ + + if (irq) + rcu_prepare_for_idle(); + rcu_dynticks_eqs_enter(); + + if (irq) + rcu_dynticks_task_enter(); +} + +/** + * rcu_nmi_exit - inform RCU of exit from NMI context + */ +void rcu_nmi_exit(void) +{ + rcu_nmi_exit_common(false); } /** @@ -824,14 +839,8 @@ void rcu_nmi_exit(void) */ void rcu_irq_exit(void) { - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); - lockdep_assert_irqs_disabled(); - if (rdtp->dynticks_nmi_nesting == 1) - rcu_prepare_for_idle(); - rcu_nmi_exit(); - if (rdtp->dynticks_nmi_nesting == 0) - rcu_dynticks_task_enter(); + rcu_nmi_exit_common(true); } /* @@ -914,7 +923,7 @@ void rcu_user_exit(void) #endif /* CONFIG_NO_HZ_FULL */ /** - * rcu_nmi_enter - inform RCU of entry to NMI context + * rcu_nmi_enter_common - inform RCU of entry to NMI context * * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know @@ -922,10 +931,10 @@ void rcu_user_exit(void) * long as the nesting level does not overflow an int. (You will probably * run out of stack space first.) * - * If you add or remove a call to rcu_nmi_enter(), be sure to test + * If you add or remove a call to rcu_nmi_enter_common(), be sure to test * with CONFIG_RCU_EQS_DEBUG=y. */ -void rcu_nmi_enter(void) +static __always_inline void rcu_nmi_enter_common(bool irq) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); long incby = 2; @@ -942,7 +951,15 @@ void rcu_nmi_enter(void) * period (observation due to Andy Lutomirski). */ if (rcu_dynticks_curr_cpu_in_eqs()) { + + if (irq) + rcu_dynticks_task_exit(); + rcu_dynticks_eqs_exit(); + + if (irq) + rcu_cleanup_after_idle(); + incby = 1; } trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), @@ -954,6 +971,14 @@ void rcu_nmi_enter(void) } /** + * rcu_nmi_enter - inform RCU of entry to NMI context + */ +void rcu_nmi_enter(void) +{ + rcu_nmi_enter_common(false); +} + +/** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle * * Enter an interrupt handler, which might possibly result in exiting @@ -977,14 +1002,8 @@ void rcu_nmi_enter(void) */ void rcu_irq_enter(void) { - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); - lockdep_assert_irqs_disabled(); - if (rdtp->dynticks_nmi_nesting == 0) - rcu_dynticks_task_exit(); - rcu_nmi_enter(); - if (rdtp->dynticks_nmi_nesting == 1) - rcu_cleanup_after_idle(); + rcu_nmi_enter_common(true); } /* -- 1.9.1