From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760455AbcLWRQR (ORCPT ); Fri, 23 Dec 2016 12:16:17 -0500 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:48154 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755000AbcLWRQQ (ORCPT ); Fri, 23 Dec 2016 12:16:16 -0500 Date: Fri, 23 Dec 2016 09:16:25 -0800 From: "Paul E. McKenney" To: Matt Fleming Cc: linux-kernel@vger.kernel.org, Mel Gorman Subject: Re: [PATCH] rcu: Enable RCU tracepoints by default to aid in debugging Reply-To: paulmck@linux.vnet.ibm.com References: <20161223151753.22745-1-matt@codeblueprint.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161223151753.22745-1-matt@codeblueprint.co.uk> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16122317-0028-0000-0000-00000651A0F7 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006303; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000198; SDB=6.00798002; UDB=6.00387473; IPR=6.00575809; BA=6.00005003; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013701; XFM=3.00000011; UTC=2016-12-23 17:16:13 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16122317-0029-0000-0000-000031E0875B Message-Id: <20161223171625.GY3924@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-12-23_14:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1612050000 definitions=main-1612230280 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Dec 23, 2016 at 03:17:53PM +0000, Matt Fleming wrote: > While debugging a performance issue I needed to understand why > RCU sofitrqs were firing so frequently. > > Unfortunately, the RCU callback tracepoints are hidden behind > CONFIG_RCU_TRACE which defaults to off in the upstream kernel and is > likely to also be disabled in enterprise distribution configs. > > Enable it by default for CONFIG_TREE_RCU. However, we must keep it > disabled for tiny RCU, because it would otherwise pull in a large > amount of code that would make tiny RCU less than tiny. > > I ran some file system metadata intensive workloads (git checkout, > FS-Mark) on a variety of machines with this patch and saw no > detectable change in performance. > > Cc: Mel Gorman > Signed-off-by: Matt Fleming Queued for testing and review, thank you! Thanx, Paul > --- > lib/Kconfig.debug | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug > index a6c8db1d62f6..7fe1ff001792 100644 > --- a/lib/Kconfig.debug > +++ b/lib/Kconfig.debug > @@ -1431,6 +1431,7 @@ config RCU_CPU_STALL_TIMEOUT > config RCU_TRACE > bool "Enable tracing for RCU" > depends on DEBUG_KERNEL > + default y if TREE_RCU > select TRACE_CLOCK > help > This option provides tracing in RCU which presents stats > -- > 2.10.0 >