From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751970AbdIUPbm (ORCPT ); Thu, 21 Sep 2017 11:31:42 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:42341 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751811AbdIUPbi (ORCPT ); Thu, 21 Sep 2017 11:31:38 -0400 Date: Thu, 21 Sep 2017 08:31:34 -0700 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Steven Rostedt , Neeraj Upadhyay , josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, linux-kernel@vger.kernel.org, sramana@codeaurora.org, prsood@codeaurora.org, pkondeti@codeaurora.org, markivx@codeaurora.org Subject: Re: Query regarding synchronize_sched_expedited and resched_cpu Reply-To: paulmck@linux.vnet.ibm.com References: <8f33e48e-ac6d-2c88-e16f-20b698c06292@codeaurora.org> <20170917010015.GW3521@linux.vnet.ibm.com> <20170918111105.15f687da@gandalf.local.home> <20170921135546.x3q3zeicbo2vtjvk@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170921135546.x3q3zeicbo2vtjvk@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 17092115-0044-0000-0000-0000039371DF X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00007773; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000231; SDB=6.00920285; UDB=6.00462418; IPR=6.00700507; BA=6.00005601; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00017237; XFM=3.00000015; UTC=2017-09-21 15:31:36 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 17092115-0045-0000-0000-000007C275EC Message-Id: <20170921153134.GG3521@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2017-09-21_02:,, 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=8.0.1-1707230000 definitions=main-1709210207 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 21, 2017 at 03:55:46PM +0200, Peter Zijlstra wrote: > On Mon, Sep 18, 2017 at 11:11:05AM -0400, Steven Rostedt wrote: > > On Sun, 17 Sep 2017 11:37:06 +0530 > > Neeraj Upadhyay wrote: > > > > > Hi Paul, how about replacing raw_spin_trylock_irqsave with > > > raw_spin_lock_irqsave in resched_cpu()? Are there any paths > > > in RCU code, which depend on trylock check/spinlock recursion? > > > > It looks to me that resched_cpu() was added for nohz full sched > > balancing, but is not longer used by that. The only user is currently > > RCU. Perhaps we should change that from a trylock to a lock. > > No, regular NOHZ balancing. NOHZ FULL wasn't conceived back then. > > 46cb4b7c88fa ("sched: dynticks idle load balancing") > > And yeah, its no longer used for that. > > And given RCU is the only user of that thing, I suppose we can indeed > change it to a full lock. Thank you! May I have your ack? Thanx, Paul