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

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Message-ID: <20071210112832.GA20189@elte.hu>
Date:	Mon, 10 Dec 2007 12:28:32 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Jiri Slaby <jirislaby@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Dipankar Sarma <dipankar@...ibm.com>
Subject: Re: broken suspend (sched related) [Was: 2.6.24-rc4-mm1]


* Gautham R Shenoy <ego@...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
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