From: Gautham R Shenoy <ego@linux.vnet.ibm.com>
To: Tejun Heo <htejun@gmail.com>
Cc: Gautham R Shenoy <ego@linux.vnet.ibm.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
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,
kernel-team@fb.com
Subject: Re: [PATCH 1/2] workqueue: Move wq_update_unbound_numa() to the beginning of CPU_ONLINE
Date: Tue, 21 Jun 2016 19:42:31 +0530 [thread overview]
Message-ID: <20160621141231.GA30251@in.ibm.com> (raw)
In-Reply-To: <20160616193504.GB3262@mtj.duckdns.org>
Hi Tejun,
On Thu, Jun 16, 2016 at 03:35:04PM -0400, Tejun Heo wrote:
> Hello,
>
> So, the issue of the initial worker not having its affinity set
> correctly wasn't caused by the order of the operations. Reordering
> just made set_cpus_allowed tried one more time late enough so that it
> hides the race condition most of the time. The problem is that
> CPU_ONLINE callbacks are called while the cpu being onlined is online
> but not active and select_fallback_rq() only considers active cpus, so
> if a kthread gets scheduled in the meantime and it doesn't have any
> cpu which is active in its allowed mask, it's allowed mask gets reset
> to cpu_possible_mask.
>
> Would something like the following make sense?
>
> Thanks.
> ------ 8< ------
> Subject: [PATCH] sched: allow kthreads to fallback to online && !active cpus
>
> During CPU hotplug, CPU_ONLINE callbacks are run while the CPU is
> online but not active. A CPU_ONLINE callback may create or bind a
> kthread so that its cpus_allowed mask only allows the CPU which is
> being brought online. The kthread may start executing before the CPU
> is made active and can end up in select_fallback_rq().
>
> In such cases, the expected behavior is selecting the CPU which is
> coming online; however, because select_fallback_rq() only chooses from
> active CPUs, it determines that the task doesn't have any viable CPU
> in its allowed mask and ends up overriding it to cpu_possible_mask.
>
> CPU_ONLINE callbacks should be able to put kthreads on the CPU which
> is coming online. Update select_fallback_rq() so that it follows
> cpu_online() rather than cpu_active() for kthreads.
>
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Reported-by: Gautham R Shenoy <ego@linux.vnet.ibm.com>
Hi Tejun,
This patch fixes the issue on POWER. I am able to see the worker
threads of the unbound workqueues of the newly onlined node with this.
Tested-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com>
> ---
> kernel/sched/core.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 017d539..a12e3db 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -1536,7 +1536,9 @@ static int select_fallback_rq(int cpu, struct task_struct *p)
> for (;;) {
> /* Any allowed, online CPU? */
> for_each_cpu(dest_cpu, tsk_cpus_allowed(p)) {
> - if (!cpu_active(dest_cpu))
> + if (!(p->flags & PF_KTHREAD) && !cpu_active(dest_cpu))
> + continue;
> + if (!cpu_online(dest_cpu))
> continue;
> goto out;
> }
>
next prev parent reply other threads:[~2016-06-21 14:12 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 [this message]
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
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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