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

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Date:	Fri, 27 Feb 2009 12:14:01 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	"Dominique Toupin" <dominique.toupin@...csson.com>
Cc:	kosaki.motohiro@...fujitsu.com,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Mathieu Desnoyers" <compudj@...stal.dyndns.org>,
	"Frederic Weisbecker" <fweisbec@...il.com>,
	"Jason Baron" <jbaron@...hat.com>,
	"Masami Hiramatsu" <mhiramat@...hat.com>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Frank Ch. Eigler" <fche@...hat.com>, <mingo@...e.hu>,
	<linux-kernel@...r.kernel.org>, <acme@...stprotocols.net>
Subject: Re: [PATCH] new irq tracer

> > > Given this scenario :
> > > 
> > > A telecommunication system runs, but the client notices 
> > something wrong.
> > > They call their service provider. The provider enables tracing 
> > > _remotely_ on the _production system_ while it's _active in 
> > the field_.
> > > 
> > > Bam, those few milliseconds interrupt latencies become unacceptable.
> > > 
> > > Hopefully this scenario makes the use-case clearer. The 
> > problem is not 
> > > that interrupt latencies would occur while tracing is on, 
> > but rather 
> > > that it would happen on a running production system when switching 
> > > tracing on. This is what is totally unacceptable for this use-case.
> > > 
> > > For more details about such requirements, I'm CCing 
> > Dominique Toupin 
> > > from Ericsson who I'm sure would be happy to give more 
> > details about 
> > > this if needed.
> > 
> > Hmm, so this system in the field is running Linux with the 
> > Real-Time Patch?  Because if it isn't it will suffer from 
> > millisecond latencies in normal operation.
>
> In many cases we don't use Linux real-time, we have many systems that
> are soft-real-time an non real-time Linux is good enough.
>  

Agreed, rt-patch seems off topics. we discuss to mainline kernel.

Steven, I sitll think nobody use ftrace on production system now yet.
Do you know actual production user?




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