From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Tejun Heo <htejun@gmail.com>,
Michael Ellerman <mpe@ellerman.id.au>,
Abdul Haleem <abdhalee@linux.vnet.ibm.com>,
Aneesh Kumar <aneesh.kumar@linux.vnet.ibm.com>,
linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a node with 1 online CPU
Date: Wed, 15 Jun 2016 18:20:33 +0530 [thread overview]
Message-ID: <20160615125033.GB31671@in.ibm.com> (raw)
In-Reply-To: <20160615113249.GH30909@twins.programming.kicks-ass.net>
On Wed, Jun 15, 2016 at 01:32:49PM +0200, Peter Zijlstra wrote:
> On Wed, Jun 15, 2016 at 03:49:36PM +0530, Gautham R Shenoy wrote:
>
> > Also, with the first patch in the series (which ensures that
> > restore_unbound_workers are called *after* the new workers for the
> > newly onlined CPUs are created) and without this one, you can
> > reproduce this WARN_ON on both x86 and PPC by offlining all the CPUs
> > of a node and bringing just one of them online.
>
> Ah good.
>
> > I am not sure about that. The workqueue creates unbound workers for a
> > node via wq_update_unbound_numa() whenever the first CPU of every node
> > comes online. So that seems legitimate. It then tries to affine these
> > workers to the cpumask of that node. Again this seems right. As an
> > optimization, it does this only when the first CPU of the node comes
> > online. Since this online CPU is not yet active, and since
> > nr_cpus_allowed > 1, we will hit the WARN_ON().
>
> So I had another look and isn't the below a much simpler solution?
>
> It seems to work on my x86 with:
>
> for i in /sys/devices/system/cpu/cpu*/online ; do echo 0 > $i ; done
> for i in /sys/devices/system/cpu/cpu*/online ; do echo 1 > $i ; done
>
> without complaint.
Yup. This will work on PPC as well.
We will no longer have the optimization in
restore_unbound_workers_cpumask() but I suppose we don't lose much by
resetting the affinity every time a CPU in the pool->attr->cpumask
comes online.
--
Thanks and Regards
gautham.
next prev parent reply other threads:[~2016-06-15 12:51 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-19 10:57 WARNING at kernel/sched/core.c:1166 while booting 4.6.0 mainline on ppc64le bare metal abdhalee
2016-05-19 12:34 ` Gavin Shan
2016-05-26 15:11 ` Gautham R Shenoy
2016-06-07 12:29 ` Abdul Haleem
2016-06-07 15:14 ` [PATCH 0/2] Fix CPU Online handling for unbounded worker threads Gautham R. Shenoy
2016-06-07 15:14 ` [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the beginning of CPU_ONLINE Gautham R. Shenoy
2016-06-15 15:53 ` Tejun Heo
2016-06-15 19:28 ` Gautham R Shenoy
2016-06-16 19:35 ` Tejun Heo
2016-06-21 14:12 ` Gautham R Shenoy
2016-06-21 15:36 ` Tejun Heo
2016-06-21 19:37 ` Peter Zijlstra
2016-06-21 19:43 ` Tejun Heo
2016-06-21 19:47 ` Peter Zijlstra
2016-06-22 5:15 ` Gautham R Shenoy
2016-06-07 15:14 ` [PATCH 2/2] workqueue:Fix affinity of an unbound worker of a node with 1 online CPU Gautham R. Shenoy
2016-06-08 6:03 ` Abdul Haleem
2016-06-14 11:22 ` Peter Zijlstra
2016-06-15 10:19 ` Gautham R Shenoy
2016-06-15 11:32 ` Peter Zijlstra
2016-06-15 12:50 ` Gautham R Shenoy [this message]
2016-06-15 13:14 ` Peter Zijlstra
2016-06-15 16:01 ` Tejun Heo
2016-06-16 12:11 ` Michael Ellerman
2016-06-16 12:45 ` Peter Zijlstra
2016-06-16 19:39 ` Tejun Heo
2016-06-17 1:49 ` Michael Ellerman
2016-07-15 5:27 ` Gautham R Shenoy
2016-07-15 5:30 ` Michael Ellerman
[not found] ` <57887507.911f240a.687de.08c5SMTPIN_ADDED_BROKEN@mx.google.com>
2016-07-15 12:10 ` Tejun Heo
2016-06-13 5:44 ` [PATCH 0/2] Fix CPU Online handling for unbounded worker threads Gautham R Shenoy
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