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    SubjectRe: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread
    On Wed, 23 Feb 2011, Mathieu Desnoyers wrote:

    > > > > +
    > > > > + local_irq_save(flags);
    > > > > + cpu = smp_processor_id();

    Drop this line.

    > > > > + if (per_cpu(rcu_cpu_kthread_task, cpu) == NULL) {

    use this_cpu_read(rcu_cpu_kthread_task)

    > > > > + local_irq_restore(flags);
    > > > > + return;
    > > > > + }
    > > > > + per_cpu(rcu_cpu_has_work, cpu) = 1;

    this_cpu_write(rcu_cpu_has_work, 1);

    > This is not quite true on x86_64 and s390 anymore. __get_cpu_var() now
    > uses a segment selector override to get the local CPU variable on x86.
    > See x86's percpu.h for details.

    __get_cpu_var cannot use a segment override since there are places where
    the address of the variable is taken. One needs to use this_cpu_ops for
    that.


    > > True, but we could also argue that the multiple checks for being preempt
    > > can also be an issue.
    >
    > At least on x86 preemption don't actually need to be disabled: selection
    > of the right per-cpu memory location is done atomically with the rest of
    > the instruction by the segment selector.

    Right.


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