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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 9FA2EC4360F for ; Tue, 2 Apr 2019 14:38:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7494920857 for ; Tue, 2 Apr 2019 14:38:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731153AbfDBOiC (ORCPT ); Tue, 2 Apr 2019 10:38:02 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34078 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726558AbfDBOiC (ORCPT ); Tue, 2 Apr 2019 10:38:02 -0400 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x32EXpdO049122 for ; Tue, 2 Apr 2019 10:38:00 -0400 Received: from e16.ny.us.ibm.com (e16.ny.us.ibm.com [129.33.205.206]) by mx0a-001b2d01.pphosted.com with ESMTP id 2rm9e0s317-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Tue, 02 Apr 2019 10:38:00 -0400 Received: from localhost by e16.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 2 Apr 2019 15:37:59 +0100 Received: from b01cxnp22036.gho.pok.ibm.com (9.57.198.26) by e16.ny.us.ibm.com (146.89.104.203) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Tue, 2 Apr 2019 15:37:54 +0100 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x32Ebrp323134322 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 2 Apr 2019 14:37:53 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C064DB2067; Tue, 2 Apr 2019 14:37:53 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A0815B2065; Tue, 2 Apr 2019 14:37:53 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.188]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Tue, 2 Apr 2019 14:37:53 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id BA2D916C2A3D; Tue, 2 Apr 2019 07:37:58 -0700 (PDT) Date: Tue, 2 Apr 2019 07:37:58 -0700 From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, 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 Subject: [PATCH RFC v2 tip/core/rcu 0/4] Real-time elimination of RCU_SOFTIRQ Reply-To: paulmck@linux.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-GCONF: 00 x-cbid: 19040214-0072-0000-0000-00000414707D X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00010861; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000284; SDB=6.01183287; UDB=6.00619479; IPR=6.00964035; MB=3.00026261; MTD=3.00000008; XFM=3.00000015; UTC=2019-04-02 14:37:58 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19040214-0073-0000-0000-00004BAF84F8 Message-Id: <20190402143758.GA15134@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-04-02_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=38 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=581 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1904020099 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! This series is v2 of an early posting of code to add a boot-time option to move RCU's softirq processing to per-CPU kthreads. This is not done by default for performance reasons, nor are these reasons theoretical. In fact, earlier attempts to do just this were not met with silence. The patches are as follows: 1. Enable elimination of Tree-RCU softirq processing via a new rcutree.use_softirq kernel boot parameter. This defaults to 1, so boot with "rcutree.use_softirq=0" to move RCU_SOFTIRQ work to the rcuc kthreads. Courtesy of Sebastian Andrzej Siewior. 2. Improve wakeup-safety checks in rcu_read_unlock_special(), thus allowing both rcuc kthreads and reasonably snappy expedited RCU grace periods. 3. Only do rcu_read_unlock_special() wakeups if expedited. 4. Allow rcu_read_unlock_special() to raise_softirq() if in_irq(). Changes since v1: o Inspired by feedback from Peter Zijlstra, avoid expensive wakeups unless there is a high probability that the current task or CPU is blocking an expedited grace period. o Account for the possibility of long-term scheduling-clock-free kernel sojourns in NO_HZ_FULL kernels. o As an exception to the above, allow use of raise_softirq_irqoff() when in an interrupt handler, in which case this is an extremely low-overhead option. Thanx, Paul ------------------------------------------------------------------------ Documentation/admin-guide/kernel-parameters.txt | 6 include/linux/sched.h | 2 kernel/rcu/tree.c | 138 +++++++++++++++++-- kernel/rcu/tree.h | 2 kernel/rcu/tree_plugin.h | 167 +++++------------------- 5 files changed, 172 insertions(+), 143 deletions(-)