From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3xXTqs1CyLzDqHj for ; Wed, 16 Aug 2017 22:56:24 +1000 (AEST) Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v7GCrqCI071601 for ; Wed, 16 Aug 2017 08:56:22 -0400 Received: from e13.ny.us.ibm.com (e13.ny.us.ibm.com [129.33.205.203]) by mx0b-001b2d01.pphosted.com with ESMTP id 2cckrcuq5m-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 16 Aug 2017 08:56:22 -0400 Received: from localhost by e13.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 16 Aug 2017 08:56:21 -0400 Date: Wed, 16 Aug 2017 05:56:17 -0700 From: "Paul E. McKenney" To: Michael Ellerman Cc: Jonathan Cameron , dzickus@redhat.com, sfr@canb.auug.org.au, linuxarm@huawei.com, Nicholas Piggin , abdhalee@linux.vnet.ibm.com, tglx@linutronix.de, sparclinux@vger.kernel.org, akpm@linux-foundation.org, linuxppc-dev@lists.ozlabs.org, David Miller , linux-arm-kernel@lists.infradead.org Subject: Re: RCU lockup issues when CONFIG_SOFTLOCKUP_DETECTOR=n - any one else seeing this? Reply-To: paulmck@linux.vnet.ibm.com References: <20170728165529.GF3730@linux.vnet.ibm.com> <20170728182053.000072aa@huawei.com> <20170728190349.GM3730@linux.vnet.ibm.com> <20170731120847.00003d5c@huawei.com> <20170731150411.GA3730@linux.vnet.ibm.com> <20170731162757.000058ba@huawei.com> <20170801184646.GE3730@linux.vnet.ibm.com> <20170802172555.0000468a@huawei.com> <20170815154743.GK7017@linux.vnet.ibm.com> <87wp63smwn.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <87wp63smwn.fsf@concordia.ellerman.id.au> Message-Id: <20170816125617.GY7017@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, Aug 16, 2017 at 10:43:52PM +1000, Michael Ellerman wrote: > "Paul E. McKenney" writes: > ... > > > > commit 33103e7b1f89ef432dfe3337d2a6932cdf5c1312 > > Author: Paul E. McKenney > > Date: Mon Aug 14 08:54:39 2017 -0700 > > > > EXP: Trace tick return from tick_nohz_stop_sched_tick > > > > Signed-off-by: Paul E. McKenney > > > > diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c > > index c7a899c5ce64..7358a5073dfb 100644 > > --- a/kernel/time/tick-sched.c > > +++ b/kernel/time/tick-sched.c > > @@ -817,6 +817,7 @@ static ktime_t tick_nohz_stop_sched_tick(struct tick_sched *ts, > > * (not only the tick). > > */ > > ts->sleep_length = ktime_sub(dev->next_event, now); > > + trace_printk("tick_nohz_stop_sched_tick: %lld\n", (tick - ktime_get()) / 1000); > > return tick; > > } > > Should I be seeing negative values? A small sample: Maybe due to hypervisor preemption delays, but I confess that I am surprised to see them this large. 1,602,250,019 microseconds is something like a half hour, which could result in stall warnings all by itself. > -0 [015] d... 1602.039695: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250019 > -0 [009] d... 1602.039701: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250025 > -0 [007] d... 1602.039702: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250025 > -0 [048] d... 1602.039703: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: 9973 > -0 [006] d... 1602.039704: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250027 > -0 [001] d... 1602.039730: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250053 > -0 [008] d... 1602.039732: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602250055 > -0 [006] d... 1602.049695: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602260018 > -0 [009] d... 1602.049695: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602260018 > -0 [001] d... 1602.049695: __tick_nohz_idle_enter: tick_nohz_stop_sched_tick: -1602260018 > > > I have a full trace, I'll send it to you off-list. I will take a look! Thanx, Paul