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

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Message-ID: <20071018062945.GA15281@in.ibm.com>
Date:	Thu, 18 Oct 2007 11:59:45 +0530
From:	Gautham R Shenoy <ego@...ibm.com>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Oleg Nesterov <oleg@...sign.ru>, Ingo Molnar <mingo@...e.hu>,
	Paul E McKenney <paulmck@...ibm.com>
Subject: Re: [RFC PATCH 1/4] Refcount Based Cpu-Hotplug Implementation

On Wed, Oct 17, 2007 at 04:29:12PM +1000, Rusty Russell wrote:
> On Wednesday 17 October 2007 15:37:54 Gautham R Shenoy wrote:
> > 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 ?
> 
> Yes.  AFAICT you use this completion on every hotplug.  Yet once a completion 
> is completed, it needs to be re-initialized to be reused: it's "complete" and 
> wait_for_completion will return immediately thereafter.
>

Okay, I thought completion followed the spinlock semantics, and hence 
didn't require re-initalization. Thanks for that information!

> Perhaps you want a waitqueue instead?

Yes, I had considered it. But completion looked appealing since it 
already had the wait-queuing code. I'll give it a try and repost 
the series with other changes.

> 
> 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!"
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