From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [patch V2 08/10] timer: Implement the hierarchical pull model
Date: Wed, 19 Apr 2017 10:31:08 +0200 (CEST)
Message-ID: <alpine.DEB.2.20.1704191028230.1829@nanos>
References: <20170418111102.490432548@linutronix.de> <20170418111401.016420305@linutronix.de> <20170419081116.GA3029@worktop.programming.kicks-ass.net>
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To: Peter Zijlstra <peterz@infradead.org>
Cc: LKML <linux-kernel@vger.kernel.org>, John Stultz <john.stultz@linaro.org>, Eric Dumazet <edumazet@google.com>, Anna-Maria Gleixner <anna-maria@linutronix.de>, "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>, linux-pm@vger.kernel.org, Arjan van de Ven <arjan@infradead.org>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Frederic Weisbecker <fweisbec@gmail.com>, Rik van Riel <riel@redhat.com>

On Wed, 19 Apr 2017, Peter Zijlstra wrote:
> On Tue, Apr 18, 2017 at 01:11:10PM +0200, Thomas Gleixner wrote:
> > +static struct tmigr_group *tmigr_get_group(unsigned int node, unsigned int lvl)
> > +{
> > +	struct tmigr_group *group;
> > +
> > +	/* Try to attach to an exisiting group first */
> > +	list_for_each_entry(group, &tmigr_level_list[lvl], list) {
> > +		/*
> > +		 * If @lvl is below the cross numa node level, check
> > +		 * whether this group belongs to the same numa node.
> > +		 */
> > +		if (lvl < tmigr_crossnode_level && group->numa_node != node)
> > +			continue;
> > +		/* If the group has capacity, use it */
> > +		if (group->num_childs < tmigr_childs_per_group) {
> > +			group->num_childs++;
> > +			return group;
> > +		}
> 
> This would result in SMT siblings not sharing groups on regular Intel
> systems, right? Since they get enumerated last.

Indeed. Will fix.

> > +	}
> > +	/* Allocate and set up a new group */
> > +	group = kzalloc_node(sizeof(*group), GFP_KERNEL, node);
> > +	if (!group)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	if (!zalloc_cpumask_var_node(&group->cpus, GFP_KERNEL, node)) {
> > +		kfree(group);
> > +		return ERR_PTR(-ENOMEM);
> > +	}
> 
> So if you place that cpumask last, you can do:
> 
> 	group = kzalloc_node(sizeof(*group) + cpumask_size(),
> 	                     GFP_KERNEL, node);

Hrm, that would allocate extra space for CPUMASK_OFF_STACK=n. I'll have a
look.

Thanks,

	tglx