Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755245AbdDQXrB (ORCPT ); Mon, 17 Apr 2017 19:47:01 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:48208 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755948AbdDQXpm (ORCPT ); Mon, 17 Apr 2017 19:45:42 -0400 From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: 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, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH v2 tip/core/rcu 12/39] rcu: Default RCU_FANOUT_LEAF to 16 unless explicitly changed Date: Mon, 17 Apr 2017 16:44:59 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20170417234452.GB19013@linux.vnet.ibm.com> References: <20170417234452.GB19013@linux.vnet.ibm.com> X-TM-AS-GCONF: 00 x-cbid: 17041723-0052-0000-0000-000001DACAEC X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006935; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000208; SDB=6.00848869; UDB=6.00419099; IPR=6.00627510; BA=6.00005292; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00015073; XFM=3.00000013; UTC=2017-04-17 23:45:36 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17041723-0053-0000-0000-000050058717 Message-Id: <1492472726-3841-12-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-04-17_20:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=1 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1702020001 definitions=main-1704170205 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1171 Lines: 33 If the RCU_EXPERT Kconfig option is not set (the default), then the RCU_FANOUT_LEAF Kconfig option will not be defined, which will cause the leaf-level rcu_node tree fanout to default to 32 on 32-bit systems and 64 on 64-bit systems. This can result in excessive lock contention. This commit therefore changes the computation of the leaf-level rcu_node tree fanout so that the result will be 16 unless an explicit Kconfig or kernel-boot setting says otherwise. Reported-by: Peter Zijlstra Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.h | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index d2f276fc2edc..376c01e539c7 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -52,11 +52,7 @@ #ifdef CONFIG_RCU_FANOUT_LEAF #define RCU_FANOUT_LEAF CONFIG_RCU_FANOUT_LEAF #else /* #ifdef CONFIG_RCU_FANOUT_LEAF */ -# ifdef CONFIG_64BIT -# define RCU_FANOUT_LEAF 64 -# else -# define RCU_FANOUT_LEAF 32 -# endif +#define RCU_FANOUT_LEAF 16 #endif /* #else #ifdef CONFIG_RCU_FANOUT_LEAF */ #define RCU_FANOUT_1 (RCU_FANOUT_LEAF) -- 2.5.2