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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 A86D6C19759 for ; Thu, 1 Aug 2019 23:08:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 878542080C for ; Thu, 1 Aug 2019 23:08:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390249AbfHAXIT (ORCPT ); Thu, 1 Aug 2019 19:08:19 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:8122 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390238AbfHAXIT (ORCPT ); Thu, 1 Aug 2019 19:08:19 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x71N7DGT040238 for ; Thu, 1 Aug 2019 19:08:18 -0400 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0a-001b2d01.pphosted.com with ESMTP id 2u475rvh5x-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 01 Aug 2019 19:08:18 -0400 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 2 Aug 2019 00:08:17 +0100 Received: from b01cxnp22036.gho.pok.ibm.com (9.57.198.26) by e13.ny.us.ibm.com (146.89.104.200) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 2 Aug 2019 00:08:12 +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 x71N8Aoq13107718 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 1 Aug 2019 23:08:11 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id D759FB206A; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B887BB2066; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 1 Aug 2019 23:08:10 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 2631416C9A47; Thu, 1 Aug 2019 16:08:12 -0700 (PDT) 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, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 04/18] rcu/nocb: Make rcutree_migrate_callbacks() start at leaf rcu_node structure Date: Thu, 1 Aug 2019 16:07:56 -0700 X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801230744.GA19115@linux.ibm.com> References: <20190801230744.GA19115@linux.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 19080123-0064-0000-0000-0000040579E2 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00011535; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000287; SDB=6.01240744; UDB=6.00654300; IPR=6.01022168; MB=3.00028000; MTD=3.00000008; XFM=3.00000015; UTC=2019-08-01 23:08:16 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19080123-0065-0000-0000-00003E81FC30 Message-Id: <20190801230810.21570-4-paulmck@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=13 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=980 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908010244 Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org Because rcutree_migrate_callbacks() is invoked infrequently and because an exact snapshot of the grace-period state might save some callbacks a second trip through a grace period, this function has used the root rcu_node structure. However, this safe-second-trip optimization happens only if rcutree_migrate_callbacks() races with grace-period initialization, so it is not worth the added mental load. This commit therefore makes rcutree_migrate_callbacks() start with the leaf rcu_node structures, as is done elsewhere. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 969ba292a669..ea479d81da7f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -3157,8 +3157,8 @@ void rcutree_migrate_callbacks(int cpu) { unsigned long flags; struct rcu_data *my_rdp; + struct rcu_node *my_rnp; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); - struct rcu_node *rnp_root = rcu_get_root(); bool needwake; if (rcu_segcblist_is_offloaded(&rdp->cblist) || @@ -3167,18 +3167,19 @@ void rcutree_migrate_callbacks(int cpu) local_irq_save(flags); my_rdp = this_cpu_ptr(&rcu_data); + my_rnp = my_rdp->mynode; if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) { local_irq_restore(flags); return; } - raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ + raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */ /* Leverage recent GPs and set GP for new callbacks. */ - needwake = rcu_advance_cbs(rnp_root, rdp) || - rcu_advance_cbs(rnp_root, my_rdp); + needwake = rcu_advance_cbs(my_rnp, rdp) || + rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist); WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); - raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags); + raw_spin_unlock_irqrestore_rcu_node(my_rnp, flags); if (needwake) rcu_gp_kthread_wake(); WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 || -- 2.17.1