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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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