linux-kernel - Re: [RFC PATCH 0/5] Refcount based Cpu Hotplug. V2

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Message-ID: <20071024181754.GC345@tv-sign.ru>
Date:	Wed, 24 Oct 2007 22:17:54 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	Christoph Lameter <clameter@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Rusty Russel <rusty@...tcorp.com.au>,
	Srivatsa Vaddagiri <vatsa@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Paul E McKenney <paulmck@...ibm.com>,
	Richard Gooch <rgooch@...f.csiro.au>,
	Tigran Aivazian <tigran@...azian.fs.co.uk>,
	Shoahua Li <shaohua.li@...ux.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Nathan Lynch <ntl@...ox.com>,
	David Miller <davem@...emloft.net>, Paul Jackson <pj@....com>,
	Josh Triplett <josh@...edesktop.org>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Akinobu Mita <akinobu.mita@...il.com>
Subject: Re: [RFC PATCH 0/5] Refcount based Cpu Hotplug. V2

On 10/24, Gautham R Shenoy wrote:
>
> On Wed, Oct 24, 2007 at 10:04:41AM -0700, Christoph Lameter wrote:
> > On Wed, 24 Oct 2007, Gautham R Shenoy wrote:
> > 
> > > This is the version 2 of the refcount based cpu-hotplug "locking" 
> > > implementation. 
> > 
> > Uggh. This introduces a global lock that has to be taken always when 
> > scanning over cpus? 
> 
> Well, no! we take the global lock only while bumping up the refcount. 
> We don't hold the lock while scanning over the cpus. And this is
> definitely an improvement over the lock_cpu_hotplug() global mutex
> we have now.

Just to be sure I didn't miss something... preempt_disable() still works,
yes?

Oleg.

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