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    SubjectRe: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier
    On Thu, Jan 07, 2010 at 09:44:15AM +0100, Peter Zijlstra wrote:
    > On Wed, 2010-01-06 at 22:35 -0800, Josh Triplett wrote:
    > >
    > > The number of threads doesn't matter nearly as much as the number of
    > > threads typically running at a time compared to the number of
    > > processors. Of course, we can't measure that as easily, but I don't
    > > know that your proposed heuristic would approximate it well.
    > Quite agreed, and not disturbing RT tasks is even more important.

    OK, so I stand un-Reviewed-by twice in one morning. ;-)

    > A simple:
    > for_each_cpu(cpu, current->mm->cpu_vm_mask) {
    > if (cpu_curr(cpu)->mm == current->mm)
    > smp_call_function_single(cpu, func, NULL, 1);
    > }
    > seems far preferable over anything else, if you really want you can use
    > a cpumask to copy cpu_vm_mask in and unset bits and use the mask with
    > smp_call_function_any(), but that includes having to allocate the
    > cpumask, which might or might not be too expensive for Mathieu.

    This would be vulnerable to the sys_membarrier() CPU seeing an old value
    of cpu_curr(cpu)->mm, and that other task seeing the old value of the
    pointer we are trying to RCU-destroy, right?

    Thanx, Paul

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      Last update: 2010-01-07 17:55    [W:0.023 / U:19.352 seconds]
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