linux-kernel - Re: [PATCH] new irq tracer

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Date:	Wed, 25 Feb 2009 17:21:47 -0500 (EST)
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <compudj@...stal.dyndns.org>
cc:	Jason Baron <jbaron@...hat.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org, acme@...stprotocols.net,
	fweisbec@...il.com
Subject: Re: [PATCH] new irq tracer



On Wed, 25 Feb 2009, Mathieu Desnoyers wrote:
> > > The main thing I dislike about only tracing action->handler() calls is
> > > that you are not tracing an IRQ per se, but rather the invocation of a
> > > given handler within the interrupt. For instance, it would be difficult
> > > to calculate the maximum interrupt latency for a given interrupt line,
> > > because you don't have the "real" irq entry/exit events, just the
> > > individual handler() calls.
> > 
> > Then use the function_graph tracer.
> > 
> 
> Sadly, the function tracer cannot be enabled on production systems.
> Therefore it's not a usable solution in the context where I need this.

And why not? It has zero overhead when disabled.

-- Steve
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