linux-kernel - Re: [PATCH 4/9] ftrace: Add enable/disable ftrace

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Date:	Mon, 28 Nov 2011 15:24:26 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jiri Olsa <jolsa@...hat.com>, fweisbec@...il.com, mingo@...hat.com,
	paulus@...ba.org, acme@...stprotocols.net,
	linux-kernel@...r.kernel.org, David Miller <davem@...emloft.net>
Subject: Re: [PATCH 4/9] ftrace: Add enable/disable ftrace_ops control
 interface

On Mon, 2011-11-28 at 21:15 +0100, Peter Zijlstra wrote:
> On Mon, 2011-11-28 at 15:12 -0500, Steven Rostedt wrote:
> > Actually, from what I've been told, x86 seems to be the only arch that
> > does crazy things with NMIs. Most the other archs do NMI when the system
> > is dead. That is, there's no return to normal system processing once an
> > NMI is hit. 
> 
> Sparc64 implements effective NMIs by playing games with their interrupt
> priority levels. local_irq_disable() disable the lower 15 (0-14) levels
> only, and their PMU interrupts at level 15.
> 
> That generates an effective NMI (interrupt not blocked by
> local_irq_disable()).

[ Added David ]

I think it's ok on sparc to modify code on one processor while another
processor is executing it. If not then we need the tricks that x86 does,
but if its ok, then we don't even need stop_machine();

-- Steve


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