From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752481AbcKZUml (ORCPT ); Sat, 26 Nov 2016 15:42:41 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:55809 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751515AbcKZUmf (ORCPT ); Sat, 26 Nov 2016 15:42:35 -0500 Date: Sat, 26 Nov 2016 04:00:46 -0800 From: "Paul E. McKenney" To: Byungchul Park Cc: josh@joshtriplett.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] rcu: Force resched_cpu when jiffies >= rcu_state.jiffies_resched Reply-To: paulmck@linux.vnet.ibm.com References: <1478673135-25509-1-git-send-email-byungchul.park@lge.com> <1478673135-25509-2-git-send-email-byungchul.park@lge.com> <20161122081220.GG2279@X58A-UD3R> <20161125083426.GC31360@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161125083426.GC31360@linux.vnet.ibm.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16112620-0028-0000-0000-00000620F4B6 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006147; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000193; SDB=6.00785739; UDB=6.00379806; IPR=6.00563361; BA=6.00004915; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013455; XFM=3.00000011; UTC=2016-11-26 20:42:32 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16112620-0029-0000-0000-00003129E472 Message-Id: <20161126120046.GA27434@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-26_13:,, 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=8.0.1-1609300000 definitions=main-1611260373 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 25, 2016 at 12:34:26AM -0800, Paul E. McKenney wrote: > On Tue, Nov 22, 2016 at 05:12:20PM +0900, Byungchul Park wrote: > > On Wed, Nov 09, 2016 at 03:32:15PM +0900, Byungchul Park wrote: > > > Currently rcu code forces CPU into scheduler when jiffies >= > > > rcu_state.gp_start + jiffies_till_sched_qs, via resched_cpu(). > > > > > > It would be better to force CPU into scheduler when jiffies >= > > > rcu_state.jiffies_resched, too. > > > > Hello, > > > > I think these two patches are necessary to call resched_cpu() even in > > case of jiffies >= rcu_state.jiffies_resched, too. Am I wrong? > > > > It would be appriciated if you let me know if I was wrong. > > My current thought is that both the "if" statement and the call to > resched_cpu() should be removed, but I am still testing and working > through the timing. > > Either way, I do very much appreciate your having called my attention > to this code! And the patch shown below seems to do the trick. Thoughts? Thanx, Paul ------------------------------------------------------------------------ commit d2db185bfee894c573faebed93461e9938bdbb61 Author: Paul E. McKenney Date: Fri Nov 25 00:07:23 2016 -0800 rcu: Remove short-term CPU kicking Commit 4914950aaa12d ("rcu: Stop treating in-kernel CPU-bound workloads as errors") added a (relatively) short-timeout call to resched_cpu(). This was inspired by as issue that was fixed by b7e7ade34e61 ("sched/core: Fix remote wakeups"). But given that this issue was fixed, it is time for the current commit to remove this call to resched_cpu(). Reported-by: Byungchul Park Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5f4f80d07852..91a68e4e6671 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1345,12 +1345,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */ } - /* And if it has been a really long time, kick the CPU as well. */ - if (ULONG_CMP_GE(jiffies, - rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) || - ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs)) - resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ - return 0; }