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Date: Thu, 10 Oct 2013 17:21:34 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>,
        Paul McKenney <paulmck@linux.vnet.ibm.com>,
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        Steven Rostedt <rostedt@goodmis.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/6] Optimize the cpu hotplug locking -v2
Message-ID: <20131010152134.GQ3081@twins.programming.kicks-ass.net>
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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?

If you can get people to agree with that I'm all for it.

That said, Oleg wants to use the same scheme for percpu_rwsem, and I'm
not sure his write-side (something in uprobes) wants to do the same.