From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752106AbaGaVyx (ORCPT ); Thu, 31 Jul 2014 17:54:53 -0400 Received: from e38.co.us.ibm.com ([32.97.110.159]:49736 "EHLO e38.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750906AbaGaVyv (ORCPT ); Thu, 31 Jul 2014 17:54:51 -0400 Date: Thu, 31 Jul 2014 14:54:46 -0700 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, laijs@cn.fujitsu.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, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com Subject: [PATCH v3 tip/core/rcu 0/9 Message-ID: <20140731215445.GA21933@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14073121-1344-0000-0000-0000032CD33A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! This series provides v3 of a prototype of an RCU-tasks implementation, which has been requested to assist with tramopoline removal. This flavor of RCU is task-based rather than CPU-based, and has voluntary context switch, usermode execution, and the idle loops as its only quiescent states. This selection of quiescent states ensures that at the end of a grace period, there will no longer be any tasks depending on a trampoline that was removed before the beginning of that grace period. This works because such trampolines do not contain function calls, do not contain voluntary context switches, do not switch to usermode, and do not switch to idle. The patches in this series are as follows: 1. Adds the basic call_rcu_tasks() functionality. 2. Provides cond_resched_rcu_qs() to force quiescent states, including RCU-tasks quiescent states, in long loops. 3. Adds synchronous APIs: synchronize_rcu_tasks() and rcu_barrier_tasks(). 4. Adds GPL exports for the above APIs, courtesy of Steven Rostedt. 5. Adds rcutorture tests for RCU-tasks. 6. Adds RCU-tasks test cases to rcutorture scripting. 7. Adds stall-warning checks for RCU-tasks. 8. Improves RCU-tasks energy efficiency by replacing polling with wait/wakeup. 9. Document RCU-tasks stall-warning messages. Changes from v2: o Use get_task_struct() instead of do_exit() hooks to synchronize with exiting tasks, as suggested by Lai Jiangshan. o Add checks of ->on_rq to the grace-period-wait polling, again as suggested by Lai Jiangshan. o Repositioned synchronize_sched() calls and improved their comments. Changes from v1: o The lockdep issue with list locking was finessed by ditching list locking in favor of having the list manipulated by a single kthread. This change trimmed about 150 highly concurrent lines from the implementation. o Get rid of the scheduler hooks in favor of polling the per-task count of voluntary context switches, in response to Peter Zijlstra's concerns about scheduler overhead. o Passes more aggressive rcutorture runs, which indicates that an increase in rcutorture's aggression is called for. o Handled review comments from Peter Zijlstra, Lai Jiangshan, Frederic Weisbecker, and Oleg Nesterov. o Added RCU-tasks stall-warning documentation. Remaining issues include: o It is not clear that trampolines in functions called from the idle loop are correctly handled. Or if anyone cares about trampolines in functions called from the idle loop. o The current implementation does not yet recognize tasks that start out executing is usermode. Instead, it waits for the next scheduling-clock tick to note them. o As a result, the current implementation does not handle nohz_full= CPUs executing tasks running in usermode. There are a couple of possible fixes under consideration. o If a task is preempted while executing in usermode, the RCU-tasks grace period will not end until that task resumes. (Is there some reasonable way to determine that a given preempted task was preempted from usermode execution?) o More about RCU-tasks needs to be added to Documentation/RCU. o This version creates rcu_tasks_kthread() even if there never will be any uses, which is expected to be the common case. A future version might create rcu_tasks_kthread() on demand, as suggested off-list by Josh Triplett. o There are probably still bugs. Thanx, Paul ------------------------------------------------------------------------ b/Documentation/RCU/stallwarn.txt | 33 - b/Documentation/kernel-parameters.txt | 5 b/fs/file.c | 2 b/include/linux/init_task.h | 9 b/include/linux/rcupdate.h | 52 + b/include/linux/sched.h | 23 b/init/Kconfig | 10 b/kernel/rcu/rcutorture.c | 44 + b/kernel/rcu/tiny.c | 2 b/kernel/rcu/tree.c | 14 b/kernel/rcu/tree_plugin.h | 2 b/kernel/rcu/update.c | 292 +++++++++- b/mm/mlock.c | 2 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS01 | 7 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS01.boot | 1 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS02 | 6 b/tools/testing/selftests/rcutorture/configs/rcu/TASKS02.boot | 1 17 files changed, 460 insertions(+), 45 deletions(-)