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

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Date:	Tue, 30 Oct 2012 13:39:47 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	linux-kernel@...r.kernel.org
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Clark Williams <clark.williams@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Mike Galbraith <efault@....de>,
	Alessio Igor Bogani <abogani@...nel.org>,
	Avi Kivity <avi@...hat.com>,
	Chris Metcalf <cmetcalf@...era.com>,
	Christoph Lameter <cl@...ux.com>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Geoff Levand <geoff@...radead.org>,
	Gilad Ben Yossef <gilad@...yossef.com>,
	Hakan Akkan <hakanakkan@...il.com>,
	Kevin Hilman <khilman@...com>,
	Stephen Hemminger <shemminger@...tta.com>,
	Sven-Thorsten Dietrich <thebigcorporation@...il.com>
Subject: Re: [PATCH 04/32] x86: New cpuset nohz irq vector

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@...il.com>
> 
> 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@...il.com>
> Cc: Alessio Igor Bogani <abogani@...nel.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Avi Kivity <avi@...hat.com>
> Cc: Chris Metcalf <cmetcalf@...era.com>
> Cc: Christoph Lameter <cl@...ux.com>
> Cc: Daniel Lezcano <daniel.lezcano@...aro.org>
> Cc: Geoff Levand <geoff@...radead.org>
> Cc: Gilad Ben Yossef <gilad@...yossef.com>
> Cc: Hakan Akkan <hakanakkan@...il.com>
> Cc: Ingo Molnar <mingo@...nel.org>
> Cc: Kevin Hilman <khilman@...com>
> Cc: Max Krasnyansky <maxk@...lcomm.com>
> Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Stephen Hemminger <shemminger@...tta.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Sven-Thorsten Dietrich <thebigcorporation@...il.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>


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