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    SubjectRe: [patch V2 08/10] timer: Implement the hierarchical pull model
    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



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