linux-kernel - Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu hotplug threads

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Date:	Thu, 14 Jun 2012 10:17:28 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [RFC patch 2/5] smpboot: Provide infrastructure for percpu
 hotplug threads

On Thu, 2012-06-14 at 10:08 +0200, Peter Zijlstra wrote:
> On Wed, 2012-06-13 at 20:56 +0200, Thomas Gleixner wrote:
> > If it's just a spurious wakeup then it goes back to sleep right away
> > as nothing cleared the park bit. 
> 
> Your spurious wakeup will have destroyed the binding though. So you need
> to be careful.

We should probably do something like the below..

TJ does this wreck workqueues? Its somewhat 'creative' in that regard
and really wants fixing.

---
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5018,6 +5018,8 @@ void do_set_cpus_allowed(struct task_str
 
 	cpumask_copy(&p->cpus_allowed, new_mask);
 	p->nr_cpus_allowed = cpumask_weight(new_mask);
+	if (p->nr_cpus_allowed != 1)
+		p->flags &= ~PF_THREAD_BOUND;
 }
 
 /*

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