From: Jay Vosburgh <jay.vosburgh@canonical.com>
To: paulmck@linux.vnet.ibm.com
Cc: Yanko Kaneti <yaneti@declera.com>,
Josh Boyer <jwboyer@fedoraproject.org>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Cong Wang <cwang@twopensource.com>, Kevin Fenzi <kevin@scrye.com>,
netdev <netdev@vger.kernel.org>,
"Linux-Kernel@Vger. Kernel. Org" <linux-kernel@vger.kernel.org>,
mroos@linux.ee, tj@kernel.org
Subject: Re: localed stuck in recent 3.18 git in copy_net_ns?
Date: Sat, 25 Oct 2014 09:38:16 -0700 [thread overview]
Message-ID: <15891.1414255096@famine> (raw)
In-Reply-To: <20141025051602.GB28247@linux.vnet.ibm.com>
Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote:
>On Fri, Oct 24, 2014 at 09:33:33PM -0700, Jay Vosburgh wrote:
>> Looking at the dmesg, the early boot messages seem to be
>> confused as to how many CPUs there are, e.g.,
>>
>> [ 0.000000] SLUB: HWalign=64, Order=0-3, MinObjects=0, CPUs=4, Nodes=1
>> [ 0.000000] Hierarchical RCU implementation.
>> [ 0.000000] RCU debugfs-based tracing is enabled.
>> [ 0.000000] RCU dyntick-idle grace-period acceleration is enabled.
>> [ 0.000000] RCU restricting CPUs from NR_CPUS=256 to nr_cpu_ids=4.
>> [ 0.000000] RCU: Adjusting geometry for rcu_fanout_leaf=16, nr_cpu_ids=4
>> [ 0.000000] NR_IRQS:16640 nr_irqs:456 0
>> [ 0.000000] Offload RCU callbacks from all CPUs
>> [ 0.000000] Offload RCU callbacks from CPUs: 0-3.
>>
>> but later shows 2:
>>
>> [ 0.233703] x86: Booting SMP configuration:
>> [ 0.236003] .... node #0, CPUs: #1
>> [ 0.255528] x86: Booted up 1 node, 2 CPUs
>>
>> In any event, the E8400 is a 2 core CPU with no hyperthreading.
>
>Well, this might explain some of the difficulties. If RCU decides to wait
>on CPUs that don't exist, we will of course get a hang. And rcu_barrier()
>was definitely expecting four CPUs.
>
>So what happens if you boot with maxcpus=2? (Or build with
>CONFIG_NR_CPUS=2.) I suspect that this might avoid the hang. If so,
>I might have some ideas for a real fix.
Booting with maxcpus=2 makes no difference (the dmesg output is
the same).
Rebuilding with CONFIG_NR_CPUS=2 makes the problem go away, and
dmesg has different CPU information at boot:
[ 0.000000] smpboot: 4 Processors exceeds NR_CPUS limit of 2
[ 0.000000] smpboot: Allowing 2 CPUs, 0 hotplug CPUs
[...]
[ 0.000000] setup_percpu: NR_CPUS:2 nr_cpumask_bits:2 nr_cpu_ids:2 nr_node_ids:1
[...]
[ 0.000000] Hierarchical RCU implementation.
[ 0.000000] RCU debugfs-based tracing is enabled.
[ 0.000000] RCU dyntick-idle grace-period acceleration is enabled.
[ 0.000000] NR_IRQS:4352 nr_irqs:440 0
[ 0.000000] Offload RCU callbacks from all CPUs
[ 0.000000] Offload RCU callbacks from CPUs: 0-1.
-J
---
-Jay Vosburgh, jay.vosburgh@canonical.com
next prev parent reply other threads:[~2014-10-25 16:38 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-10-20 20:15 localed stuck in recent 3.18 git in copy_net_ns? Kevin Fenzi
2014-10-20 20:43 ` Dave Jones
2014-10-20 20:53 ` Kevin Fenzi
2014-10-21 21:12 ` Kevin Fenzi
2014-10-22 17:12 ` Josh Boyer
2014-10-22 17:37 ` Cong Wang
2014-10-22 17:49 ` Josh Boyer
2014-10-22 17:53 ` Eric W. Biederman
2014-10-22 18:11 ` Paul E. McKenney
2014-10-22 18:25 ` Eric W. Biederman
2014-10-22 18:55 ` Paul E. McKenney
2014-10-22 19:33 ` Josh Boyer
2014-10-22 22:40 ` Yanko Kaneti
2014-10-22 23:24 ` Paul E. McKenney
2014-10-23 6:09 ` Yanko Kaneti
2014-10-23 12:27 ` Paul E. McKenney
2014-10-23 15:33 ` Paul E. McKenney
[not found] ` <CA+5PVA4H6EAf6cBc4a_8W8x4Mgppjc5GsskKaCRry2jq+LP+FA@mail.gmail.com>
2014-10-23 16:28 ` Paul E. McKenney
2014-10-23 19:51 ` Yanko Kaneti
2014-10-23 20:05 ` Paul E. McKenney
2014-10-23 21:45 ` Yanko Kaneti
2014-10-23 22:04 ` Paul E. McKenney
2014-10-24 4:48 ` Jay Vosburgh
2014-10-24 14:50 ` Paul E. McKenney
2014-10-24 18:20 ` Jay Vosburgh
2014-10-24 18:33 ` Paul E. McKenney
2014-10-24 9:08 ` Yanko Kaneti
2014-10-24 15:40 ` Paul E. McKenney
2014-10-24 16:29 ` Yanko Kaneti
2014-10-24 16:54 ` Paul E. McKenney
2014-10-24 17:09 ` Yanko Kaneti
2014-10-24 17:20 ` Paul E. McKenney
2014-10-24 17:35 ` Yanko Kaneti
2014-10-24 18:32 ` Paul E. McKenney
2014-10-24 18:49 ` Jay Vosburgh
2014-10-24 18:57 ` Paul E. McKenney
2014-10-24 20:15 ` Paul E. McKenney
2014-10-24 21:25 ` Yanko Kaneti
2014-10-24 21:49 ` Paul E. McKenney
2014-10-24 22:02 ` Jay Vosburgh
2014-10-24 22:16 ` Paul E. McKenney
2014-10-24 22:41 ` Jay Vosburgh
2014-10-24 22:34 ` Jay Vosburgh
2014-10-24 22:59 ` Paul E. McKenney
2014-10-24 23:05 ` Paul E. McKenney
2014-10-25 0:20 ` Jay Vosburgh
2014-10-25 2:03 ` Paul E. McKenney
2014-10-25 4:33 ` Jay Vosburgh
2014-10-25 5:16 ` Paul E. McKenney
2014-10-25 16:38 ` Jay Vosburgh [this message]
2014-10-25 18:18 ` Paul E. McKenney
2014-10-27 17:45 ` Paul E. McKenney
2014-10-27 20:43 ` Jay Vosburgh
2014-10-27 21:07 ` Paul E. McKenney
2014-10-28 8:12 ` Yanko Kaneti
2014-10-28 12:50 ` Paul E. McKenney
2014-10-28 13:00 ` Yanko Kaneti
2014-10-28 15:54 ` Kevin Fenzi
2014-10-28 16:15 ` Paul E. McKenney
2014-10-25 12:09 ` Yanko Kaneti
2014-10-25 13:38 ` Paul E. McKenney
2014-10-22 17:59 ` Paul E. McKenney
2014-10-22 18:03 ` Josh Boyer
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