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    SubjectRe: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier
    Mathieu Desnoyers <> writes:

    > Both the signal-based and the sys_membarrier userspace RCU schemes
    > permit us to remove the memory barrier from the userspace RCU
    > rcu_read_lock() and rcu_read_unlock() primitives, thus significantly
    > accelerating them. These memory barriers are replaced by compiler
    > barriers on the read-side, and all matching memory barriers on the
    > write-side are turned into an invokation of a memory barrier on all
    > active threads in the process. By letting the kernel perform this
    > synchronization rather than dumbly sending a signal to every process
    > threads (as we currently do), we diminish the number of unnecessary wake
    > ups and only issue the memory barriers on active threads. Non-running
    > threads do not need to execute such barrier anyway, because these are
    > implied by the scheduler context switches.

    I'm not sure all this effort is really needed on architectures
    with strong memory ordering.

    > + * The current implementation simply executes a memory barrier in an IPI handler
    > + * on each active cpu. Going through the hassle of taking run queue locks and
    > + * checking if the thread running on each online CPU belongs to the current
    > + * thread seems more heavyweight than the cost of the IPI itself.
    > + */
    > +SYSCALL_DEFINE0(membarrier)
    > +{
    > + on_each_cpu(membarrier_ipi, NULL, 1);

    Can't you use mm->cpu_vm_mask?


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      Last update: 2010-01-07 10:53    [W:0.020 / U:8.752 seconds]
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