Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

[Gautham R Shenoy <ego@in.ibm.com>]

On Wed, Oct 17, 2007 at 10:47:41AM +1000, Rusty Russell wrote:
> On Tuesday 16 October 2007 20:34:17 Gautham R Shenoy wrote:
> > This patch implements a Refcount + Waitqueue based model for
> > cpu-hotplug.
> 
> Hi Gautham,

Hi Rusty, 

> 
> 	I can't see where you re-initialize the completion.  

The cpu_hotplug.readers_done is a global variable which has been
initialized in cpu_hotplug_init. 

So I am wondering is the re-initialization required ? 

> 
> > +static void cpu_hotplug_begin(void)
> > +{
> > +	mutex_lock(&cpu_hotplug.lock);
> > +	cpu_hotplug.active_writer = current;
> > +	while (cpu_hotplug.refcount) {
> > +		mutex_unlock(&cpu_hotplug.lock);
> > +		wait_for_completion(&cpu_hotplug.readers_done);
> > +		mutex_lock(&cpu_hotplug.lock);
> > +	}
> 
> AFAICT this will busy-wait on the second CPU hotplug.
> 

Well when the first cpu_hotplug comes out of wait_for_completion, it
would have decremented the ->done count, so it's as good as new 
for the second CPU hotplug, no?

> Cheers,
> Rusty.

Thanks and Regards
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!"