linux-kernel - Re: [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core

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Message-ID: <20070217053233.GA22435@in.ibm.com>
Date:	Sat, 17 Feb 2007 11:02:33 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Srivatsa Vaddagiri <vatsa@...ibm.com>
Cc:	Oleg Nesterov <oleg@...sign.ru>, akpm@...l.org, paulmck@...ibm.com,
	mingo@...e.hu, dipankar@...ibm.com, venkatesh.pallipadi@...el.com,
	linux-kernel@...r.kernel.org, rjw@...k.pl
Subject: Re: [RFC PATCH(Experimental) 1/4] freezer-cpu-hotplug core

On Fri, Feb 16, 2007 at 01:42:09PM +0530, Srivatsa Vaddagiri wrote:
> On Fri, Feb 16, 2007 at 12:46:17PM +0530, Srivatsa Vaddagiri wrote:
> > frozen. The only exception is cleaning up of per-cpu threads (which is
> > not possible with processes frozen - if we can find a way to make that
> > possible, then everything can be done in CPU_DEAD).
> 
> How abt a patch like below?
> 
> 
> --- process.c.org	2007-02-16 13:38:39.000000000 +0530
> +++ process.c	2007-02-16 13:38:59.000000000 +0530
> @@ -47,7 +47,7 @@ void refrigerator(void)
>  	recalc_sigpending(); /* We sent fake signal, clean it up */
>  	spin_unlock_irq(&current->sighand->siglock);
> 
> -	while (frozen(current)) {
> +	while (frozen(current) && !kthread_should_stop()) {
>  		current->state = TASK_UNINTERRUPTIBLE;
>  		schedule();
>  	}

This looks ok, but probably we could do it in a better way.
How about an api to thaw only a specific task something like
thaw_process(struct task_struct p). 

That way, the CPU_DEAD handler which wants to kthread_stop a thread
can selectively thaw the thread before it does kthread_stop.

Rafael, does this have any negative impact on the freezer design?

> This should let us do kthread_stop() in CPU_DEAD itself (while processes
> are frozen)? That would allow us to do everything from CPU_DEAD itself
> (and not have CPU_DEAD_KILL_THREADS).
> 
> 
> -- 
> Regards,
> vatsa

thanks
gautham.
-- 
Gautham R Shenoy
Linux Technology Center
IBM India.
"Freedom comes with a price tag of responsibility, which is still a bargain,
because Freedom is priceless!"
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