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Date: Wed, 10 Nov 2010 19:49:31 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: "Luck, Tony" <tony.luck@intel.com>, Steven Rostedt <rostedt@goodmis.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "Huang, Ying" <ying.huang@intel.com>, "bp@alien8.de" <bp@alien8.de>,
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        Arjan van de Ven <arjan@infradead.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Subject: Re: [RFC/Requirements/Design] h/w error reporting
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* Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:

> On Wed, 2010-11-10 at 10:23 -0800, Luck, Tony wrote:
> > > A few of things that pop up quickly are:
> > >
> > > 1) lockless
> > 
> > This is a clear requirement for use in h/w error
> > reporting too.  Taking locks in NMI or machine
> > check handler isn't an option.
> 
> Don't worry, lots of PMIs are NMIs, perf needs to be fully NMI safe
> otherwise things simply don't work.

Yep, in fact perf was fully NMI safe earlier than the ftrace ring-buffer.

When perf code is NMI unsafe we notice it very quickly. I regularly record millions 
of events per second.

Thanks,

	Ingo