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Date: Mon, 10 Sep 2012 23:30:37 +0200
From: Frederic Weisbecker <fweisbec@gmail.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
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        Max Krasnyansky <maxk@qualcomm.com>,
        Stephen Hemminger <shemminger@vyatta.com>,
        Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
Subject: Re: [PATCH tip/core/rcu 08/26] x86: Syscall hooks for userspace RCU
 extended QS
Message-ID: <20120910213023.GB21277@somewhere.redhat.com>
References: <20120830210520.GA2824@linux.vnet.ibm.com>
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On Fri, Aug 31, 2012 at 04:59:10PM -0700, Josh Triplett wrote:
> On Thu, Aug 30, 2012 at 02:05:25PM -0700, Paul E. McKenney wrote:
> > From: Frederic Weisbecker <fweisbec@gmail.com>
> > 
> > Add syscall slow path hooks to notify syscall entry
> > and exit on CPUs that want to support userspace RCU
> > extended quiescent state.
> > 
> > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
> > Cc: Alessio Igor Bogani <abogani@kernel.org>
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Avi Kivity <avi@redhat.com>
> > Cc: Chris Metcalf <cmetcalf@tilera.com>
> > Cc: Christoph Lameter <cl@linux.com>
> > Cc: Geoff Levand <geoff@infradead.org>
> > Cc: Gilad Ben Yossef <gilad@benyossef.com>
> > Cc: Hakan Akkan <hakanakkan@gmail.com>
> > Cc: H. Peter Anvin <hpa@zytor.com>
> > Cc: Ingo Molnar <mingo@kernel.org>
> > Cc: Josh Triplett <josh@joshtriplett.org>
> > Cc: Kevin Hilman <khilman@ti.com>
> > Cc: Max Krasnyansky <maxk@qualcomm.com>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Stephen Hemminger <shemminger@vyatta.com>
> > Cc: Steven Rostedt <rostedt@goodmis.org>
> > Cc: Sven-Thorsten Dietrich <thebigcorporation@gmail.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> This seems reasonable; presumably you plan to add something actually
> setting TIF_NOHZ in a subsequent patch series?

Yes, currently this is set by the selftests, see the combination of:

	[PATCH tip/core/rcu 07/26] rcu: Switch task's syscall hooks on context switch
	[PATCH tip/core/rcu 14/26] rcu: Userspace RCU extended QS selftest

Later this will be driven by the nohz subsystem.