Re: [PATCH tip/core/rcu 08/26] x86: Syscall hooks for userspace RCUextended QS

From: Frederic Weisbecker
Date: Mon Sep 10 2012 - 17:38:23 EST


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@xxxxxxxxx>
> >
> > 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@xxxxxxxxx>
> > Cc: Alessio Igor Bogani <abogani@xxxxxxxxxx>
> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > Cc: Avi Kivity <avi@xxxxxxxxxx>
> > Cc: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> > Cc: Christoph Lameter <cl@xxxxxxxxx>
> > Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
> > Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
> > Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
> > Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> > Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> > Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> > Cc: Kevin Hilman <khilman@xxxxxx>
> > Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > Cc: Stephen Hemminger <shemminger@xxxxxxxxxx>
> > Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > Cc: Sven-Thorsten Dietrich <thebigcorporation@xxxxxxxxx>
> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
>
> 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.
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