Re: [PATCH 04/32] x86: New cpuset nohz irq vector

[Steven Rostedt]

On Mon, 2012-10-29 at 16:27 -0400, Steven Rostedt wrote:
> plain text document attachment
> (0004-x86-New-cpuset-nohz-irq-vector.patch)
> From: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> 
> We need a way to send an IPI (remote or local) in order to
> asynchronously restart the tick for CPUs in nohz adaptive mode.
> 
> This must be asynchronous such that we can trigger it with irqs
> disabled. This must be usable as a self-IPI as well for example
> in cases where we want to avoid random dealock scenario while
> restarting the tick inline otherwise.
> 
> This only settles the x86 backend. The core tick restart function
> will be defined in a later patch.
> 
> [CHECKME: Perhaps we instead need to use irq work for self IPIs.
> But we also need a way to send async remote IPIs.]

Probably just use irq_work for self ipis, and normal ipis for other
CPUs.

Also, what reason do we have to force a task out of nohz? IOW, do we
really need this?

Also, perhaps we could just tag onto the schedule_ipi() function instead
of having to create a new IPI for all archs?

-- Steve

> 
> 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: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
> Cc: Geoff Levand <geoff@xxxxxxxxxxxxx>
> Cc: Gilad Ben Yossef <gilad@xxxxxxxxxxxxx>
> Cc: Hakan Akkan <hakanakkan@xxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: Kevin Hilman <khilman@xxxxxx>
> Cc: Max Krasnyansky <maxk@xxxxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
> 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>


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