linux-kernel - Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

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Date:	Thu, 10 Oct 2013 10:13:53 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2

On Thu, Oct 10, 2013 at 06:50:46PM +0200, Ingo Molnar wrote:
> 
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Thu, Oct 10, 2013 at 04:57:38PM +0200, Ingo Molnar wrote:
> >
> > > So ... why not make it _really_ cheap, i.e. the read lock costing 
> > > nothing, and tie CPU hotplug to freezing all tasks in the system?
> > 
> > Such that we freeze regular tasks in userspace and kernel tasks in their 
> > special freezer callback so as to guarantee minimal state?
> 
> Yes, absolutely.

That does add quite a bit of latency to the hotplug operations, which
IIRC slows down things like boot, suspend, and resume.

							Thanx, Paul

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