Re: broken suspend (sched related) [Was: 2.6.24-rc4-mm1]

Ingo Molnar
2007-12-10T11:29:31Z

* Gautham R Shenoy <ego@in.ibm.com> wrote:

> > say we've got 100 CPUs, so we've got 100 watchdog tasks running -
> > one for each CPU. Checking for hung tasks is a global operation not
> > a per-CPU operation (we iterate over the global tasklist), hence
> > only one CPU should really be calling this function. That
> > online-cpus logic achieves this by picking a single CPU. Perhaps it
> > would be better to keep a hung_task_checker_cpu variable that is
> > driven from a CPU-hotplug-down notifier? That way if a CPU is
> > brought down we can update hung_task_checker_cpu to another,
> > still-online CPU. (this would also be faster, because event-driven)
>
> Do you mean something like this?

yeah, thanks - queued it up.

one question:

> +static int check_cpu = -1;

> case CPU_ONLINE:
> case CPU_ONLINE_FROZEN:
> + check_cpu = any_online_cpu(cpu_online_map);
> wake_up_process(per_cpu(watchdog_task, hotcpu));
> break;

do we bring the boot CPU online too - i.e. will check_cpu be properly
initialized on UP too?

Ingo