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    SubjectRe: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier
    * 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
    OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68


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