linux-kernel - Re: Fix powerTOP regression with 2.6.39-rc5

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Date:	Tue, 10 May 2011 12:13:48 -0700
From:	David Sharp <dhsharp@...gle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>,
	Michael Rubin <mrubin@...gle.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Christoph Hellwig <hch@...radead.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: Fix powerTOP regression with 2.6.39-rc5

On Tue, May 10, 2011 at 3:33 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Tue, 2011-05-10 at 10:47 +0200, Ingo Molnar wrote:
>> * Steven Rostedt <rostedt@...dmis.org> wrote:
>>
>> > [...] Thus a library is a perfect solution. [...]
>>
>> Btw., just to make things clear, if we indeed have a library to parse things
>> and if all apps use that then the ABI moves to another (library) level.
>>
>> The requirement from my maintenance POV is very, very simple: apps should not
>> break on new kernels. If this is achieved by making apps smarter then that's a
>> valid solution.
>>
>
> Great! Because this is what I want. I would also want a way to designate
> events as stable. I'll add a TRACE_EVENT_STABLE() that can only have the
> events that maintainers agree to maintain. And give the apps an ability
> to only see these.

A TRACE_EVENT_STABLE() would mark the entire event as stable. I was
wondering if we should instead mark fields within events as stable.
Even within a "stable" event, certain fields we might not want to
guarantee to be in the next release. This might also make it clearer
that the position of a field (stable or not) in an event can change,
and tools really should parse the event format.

> Have the other events need either a separate library,
> or perhaps just separate calls from within the same library, so the XFS
> developers can feel safe that their tracepoints will not be depended on.
> And perhaps have two tracepoints for sched_switch such that Peter
> Zijlsta is happy that he's not bound by an tracepoint that keeps him
> from getting rid of FIFO ;)
>
> I'm happy to write a libperf.so and I can discuss with Arnaldo, Arjan
> and yourself what is the best way of doing this.
>
> Thanks,
>
> -- Steve
>
>
>
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