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SubjectRe: [patch V2 08/10] timer: Implement the hierarchical pull model
On Wed, Apr 19, 2017 at 11:09:14AM +0200, Peter Zijlstra wrote:

> Would it be very onerous to rewrite that into regular loops? That avoids
> us having to think (and worry) about blowing our stack.

void walk_groups(bool (*up)(void *), void (*down)(void *), void *data)
{
struct tmigr_cpu *tmc = this_cpu_ptr(&tmigr_cpu);
struct group *stack[tmigr_hierarchy_levels];
struct group *group = tmc->group;
int i = 0;

raw_spin_lock(&tmc->lock);

do {
stack[i++] = group;

if (up(data))
break;

} while ((group = group->parent));

do {
group = stack[--i];

down(data);

} while (group != tmc->group);

raw_spin_unlock(&tmc->lock);
}

Something like so, iterates the hierarchy for the current CPU and calls
@up and @down at each level in the proper order. And has obvious stack
usage.

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