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

[Ingo Molnar]

* Gautham R Shenoy <ego@xxxxxxxxxx> 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
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