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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY,USER_AGENT_GIT autolearn=no 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 0AD2ECA9ED1 for ; Sat, 2 Nov 2019 12:47:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DF40F21726 for ; Sat, 2 Nov 2019 12:47:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726804AbfKBMrX (ORCPT ); Sat, 2 Nov 2019 08:47:23 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:42056 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726229AbfKBMrW (ORCPT ); Sat, 2 Nov 2019 08:47:22 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R161e4;CH=green;DM=||false|;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=laijs@linux.alibaba.com;NM=1;PH=DS;RN=9;SR=0;TI=SMTPD_---0Th-p51w_1572698837; Received: from localhost(mailfrom:laijs@linux.alibaba.com fp:SMTPD_---0Th-p51w_1572698837) by smtp.aliyun-inc.com(127.0.0.1); Sat, 02 Nov 2019 20:47:17 +0800 From: Lai Jiangshan To: linux-kernel@vger.kernel.org Cc: Lai Jiangshan , "Paul E. McKenney" , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: [PATCH V2 0/7] rcu: introduce percpu rcu_preempt_depth Date: Sat, 2 Nov 2019 12:45:52 +0000 Message-Id: <20191102124559.1135-1-laijs@linux.alibaba.com> X-Mailer: git-send-email 2.20.1 Reply-To: <20191101162109.GN20975@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Rather than using the generic version of preempt_count, x86 uses a special version of preempt_count implementation that take advantage of x86 (single instruction to access/add/decl/flip-bits of percpu counter). It makes the preempt_count operations really cheap. For x86, rcu_preempt_depth can also take the same advantage by using the same technique. After the patchset: - No function call when using rcu_read_[un]lock(). It is minor improvement, other arch can also achieve it via moving ->rcu_read_lock_nesting and ->rcu_read_unlock_special to thread_info, but inlined rcu_read_[un]lock() generates more instructions and footprint in other arch generally. - Only single instruction for rcu_read_lock(). - Only 2 instructions for the fast path of rcu_read_unlock(). Patch4 simplifies rcu_read_unlock() by avoid using negative ->rcu_read_lock_nesting, Patch7 introduces the percpu rcu_preempt_depth. Other patches are for preparation. changed from v1: drop patch1/2 of the v1 drop merged patches Using special.b.deferred_qs to avoid wakeup in v1 is changed to using preempt_count. And special.b.deferred_qs is removed. Lai Jiangshan (7): rcu: use preempt_count to test whether scheduler locks is held rcu: cleanup rcu_preempt_deferred_qs() rcu: remove useless special.b.deferred_qs rcu: don't use negative ->rcu_read_lock_nesting rcu: wrap usages of rcu_read_lock_nesting rcu: clear the special.b.need_qs in rcu_note_context_switch() x86,rcu: use percpu rcu_preempt_depth arch/x86/Kconfig | 2 + arch/x86/include/asm/rcu_preempt_depth.h | 87 +++++++++++++++++++ arch/x86/kernel/cpu/common.c | 7 ++ arch/x86/kernel/process_32.c | 2 + arch/x86/kernel/process_64.c | 2 + include/linux/rcupdate.h | 24 ++++++ include/linux/sched.h | 2 +- init/init_task.c | 2 +- kernel/fork.c | 2 +- kernel/rcu/Kconfig | 3 + kernel/rcu/tree_exp.h | 35 ++------ kernel/rcu/tree_plugin.h | 101 ++++++++++++++--------- 12 files changed, 196 insertions(+), 73 deletions(-) create mode 100644 arch/x86/include/asm/rcu_preempt_depth.h -- 2.20.1