From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932823AbcK1K6S (ORCPT ); Mon, 28 Nov 2016 05:58:18 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:36140 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932469AbcK1K6Q (ORCPT ); Mon, 28 Nov 2016 05:58:16 -0500 Date: Mon, 28 Nov 2016 02:58:09 -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> <20161126120046.GA27434@linux.vnet.ibm.com> <20161128064639.GH2279@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161128064639.GH2279@X58A-UD3R> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16112810-8235-0000-0000-000009B5FC17 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00006156; HX=3.00000240; KW=3.00000007; PH=3.00000004; SC=3.00000193; SDB=6.00786356; UDB=6.00380250; IPR=6.00564043; BA=6.00004919; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00013465; XFM=3.00000011; UTC=2016-11-28 10:58:13 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16112810-8236-0000-0000-000036D011FF Message-Id: <20161128105809.GZ31360@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-28_04:,, 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-1611280188 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 28, 2016 at 03:46:39PM +0900, Byungchul Park wrote: > On Sat, Nov 26, 2016 at 04:00:46AM -0800, Paul E. McKenney wrote: > > 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? > > Hello, > > I see.. I didn't check the log 'rcu: Stop treating in-kernel CPU-bound > workloads as errors'. > > If you are convinced to remove them, no objection. It is quite possible that additional time-related adjustments are needed, but this change is a step in the right direction. Thanx, Paul > Thank you, > Byungchul > > > > > 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; > > } > > >