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    SubjectRe: [Experimental CPU Hotplug PATCH] - Move migrate_all_tasks to CPU_DEAD handling
    On Wed, 2004-04-07 at 15:01, Srivatsa Vaddagiri wrote:
    > I restore the mask though (under covers of lock_cpu_hotplug) before
    > returning from cpu_down. Task should never see this violated affinity.

    But other tasks can do a getaffinity() on it and see the wrong affinity.
    Probably not a big issue.

    > Rusty,
    > What do you think abt the whole patch? It has withstood
    > my stress-test harness :-)

    I agree with Ingo: it's clever, well done. Minor nitpicks:

    +void migrate_all_tasks(int cpu)
    struct task_struct *tsk, *t;
    int dest_cpu, src_cpu;
    unsigned int node;

    - /* We're nailed to this CPU. */
    - src_cpu = smp_processor_id();
    + src_cpu = cpu;

    Just make the parameter name "src_cpu"?

    + /* Take idle task off runqueue and restore it's
    + * policy/priority
    + */
    + rq = task_rq_lock(rq->idle, &flags);
    + /* Call init_idle instead ?? init_idle doesn't restore
    + * policy though for us ..
    + */
    + deactivate_task(rq->idle, rq);
    + __setscheduler(rq->idle, SCHED_NORMAL, MAX_PRIO);
    + task_rq_unlock(rq, &flags);

    One-line comments and compact code good:

    /* Idle task back to normal (off runqueue, low prio) */
    rq = task_rq_lock(rq->idle, &flags);
    deactivate_task(rq->idle, rq);
    __setscheduler(rq->idle, SCHED_NORMAL, MAX_PRIO);
    task_rq_unlock(rq, &flags);

    + /* Force scheduler to switch to idle task when we yield.
    + * We expect idle task to _immediately_ notice that it's
    + * is offline and die quickly.
    + *
    + * This allows us to defer calling mirate_all_tasks
    + * CPU_DEAD notification time.
    + */
    + sched_idle_next();

    This comment's very big. They don't need to know all the things we
    don't do. I'd prefer:

    /* Force idle task to run as soon as we yield: it should
    immediately notice cpu is offline and die quickly. */

    I'm happy for this to go in..
    Anyone who quotes me in their signature is an idiot -- Rusty Russell

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