Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier

Mathieu Desnoyers
2010-01-10T01:09:55Z

* Steven Rostedt (rostedt@goodmis.org) wrote:
> On Sat, 2010-01-09 at 18:05 -0500, Steven Rostedt wrote:
>
> > Then we should have O(tasks) for spinlocks taken, and
> > O(min(tasks, CPUS)) for IPIs.
> >
>
> And for nr tasks >> CPUS, this may help too:
>
> > cpumask = 0;
> > foreach task {
>
> if (cpumask == online_cpus)
> break;

This is not required with for_each_cpu(cpu, mm_cpumask(current->mm)),
because it only iterates on active cpus on which the current process
threads are scheduled.

Thanks,

Mathieu

>
> > spin_lock(task_rq(task)->rq->lock);
> > if (task_rq(task)->curr == task)
> > cpu_set(task_cpu(task), cpumask);
> > spin_unlock(task_rq(task)->rq->lock);
> > }
> > send_ipi(cpumask);
> >
>
> -- Steve
>
>

--
Mathieu Desnoyers
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