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SubjectRe: [PATCH] sched, numa: Use {cpu, pid} to create task groups for shared faults
On Wed, Jul 31, 2013 at 05:07:51PM +0200, Peter Zijlstra wrote:
> @@ -1260,6 +1400,23 @@ void task_numa_fault(int last_cpupid, in
> }
>
> /*
> + * First accesses are treated as private, otherwise consider accesses
> + * to be private if the accessing pid has not changed
> + */
> + if (unlikely(last_cpupid == (-1 & LAST_CPUPID_MASK))) {
> + priv = 1;
> + } else {
> + int cpu, pid;
> +
> + cpu = cpupid_to_cpu(last_cpupid);
> + pid = cpupid_to_pid(last_cpupid);
> +
> + priv = (pid == (p->pid & LAST__PID_MASK));

So Rik just pointed out that this condition is likely to generate false
positives due to the birthday paradox. The problem with including
cpu/nid information is another kind of false positives.

We've no idea which is worse..

> + if (!priv)
> + task_numa_group(p, cpu, pid);
> + }


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