* Paul E. McKenney <[EMAIL PROTECTED]> wrote:
> > in fact (new) kprobes uses the freezer, and it's far more
> > performance sensitive than the handling of CPU hotplug events.
>
> Outside of realtime workloads, I agree that performance should not be
> a problem. And I don't know of any reason why realtime systems need
> to be able to do hotplug CPU. Yet, anyway. ;-)
even for -rt it's not really an issue: the hotplug locks are so
all-encompassing and so unbound at the moment that there's no realistic
expectation for them to ever become deterministic. So we might as well
make them encompass "everything" - without any noticeable effect.
> So the thought is to make _cpu_down() and _cpu_up() do something like
> the following (untested, probably does not even compile), perhaps with
> suitable adjustments elsewhere as well?
>
> static int _cpu_down(unsigned int cpu)
> {
> int err;
> struct task_struct *p;
> cpumask_t old_allowed, tmp;
>
> if (num_online_cpus() == 1)
> return -EBUSY;
>
> if (!cpu_online(cpu))
> return -EINVAL;
>
> if (freeze_processes()) {
> err = -EBUSY;
> goto out_freeze_notify_failed;
> }
> err = raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE,
> (void *)(long)cpu);
yeah. This all looks so nice that i almost cannot believe it's true :-)
This would allow us to rip out all the cpu-hotplug locking: wow! If only
someone would volunteer to try to pull this off and then to touch so
many subsystems ;-)
i fully agree that the opposite notifications should be traversed in
inverse order [but this is an orthogonal improvement]. Too bad the
notifier list is a single linked list.
Ingo
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [EMAIL PROTECTED]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
