linux-kernel - Re: LTTng finds abnormally long APIC interrupt handler : 58.2 ms

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Message-ID: <alpine.DEB.1.10.0808071429380.7625@gandalf.stny.rr.com>
Date:	Thu, 7 Aug 2008 14:32:44 -0400 (EDT)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	"Frank Ch. Eigler" <fche@...hat.com>
cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	akpm@...ux-foundation.org, Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, ltt-dev@...ts.casi.polymtl.ca
Subject: Re: LTTng finds abnormally long APIC interrupt handler : 58.2 ms


On Thu, 7 Aug 2008, Frank Ch. Eigler wrote:
> Steven Rostedt <rostedt@...dmis.org> writes:
> >
> > I've been thinking of exporting it, and make it so that once you 
> > register something to the trace_ops, I'll up the module count, and never 
> > let that module unload.
> 
> This issue will need some sort of resolution if systemtap is to be
> able to hook up to ftrace.  Perhaps we could have a second/nested API
> that suffers the costs of explicit reference counting, but does permit
> dynamic attach and robust detach.

I've also thought about having a second registration method that would 
hook the mcount function to an internal one, one that is always there. 
Here we could add logic to know that a driver has registered a function. 
It will just have the added overhead of that logic.

It's not hard to do. I just didn't want to clutter ftrace too much before 
it made it into a major release. This means any patches to do this will 
happen after 27.

-- Steve

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