linux-kernel - Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

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Date:	Wed, 24 Jul 2013 03:33:15 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Andi Kleen <andi@...stfloor.org>, Vince Weaver <vince@...ter.net>,
	Andi Kleen <ak@...ux.intel.com>, acme@...radead.org,
	mingo@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>,
	torvalds@...ux-foundation.org, trinity@...r.kernel.org
Subject: Re: [PATCH 1/2] tools, perf: Add a precise event qualifier v2

On Tue, Jul 23, 2013 at 08:39:09PM -0400, Sasha Levin wrote:
> On 07/23/2013 06:51 PM, Andi Kleen wrote:
> >On Tue, Jul 23, 2013 at 05:27:43PM -0400, Vince Weaver wrote:
> >>>
> >>>I hate having to justify why breaking the ABI is unacceptable.
> >Well it's a testing ABI, so we can do changes to it.
> 
> The testing ABI has a simple policy about changes:
> 
> 	The interface can be changed to add new features, but the
> 	current interface will not break by doing this, unless grave
> 	errors or security problems are found in them.
> 
> It's probably fine to change a testing ABI once in a while, but when things
> like trinity start breaking that often due to ABI changes in the same exact
> place, that's too much IMO.

It sounds like trinity is breaking (well printing a message, not really
breaking) on any addition. So if we follow that the perf sysfs interface
would be completely frozen and can never be extended over today.

I don't think it's a big problem that a test tool needs to be extended
when the software it's testing changes.

If there are enough other widely used programs that actually break from
additions probably would need a v2 of the sysfs interface for extensions
(with new file or directory names), and keep v1 frozen for
compatibility. 

But I don't think that's the case today?

-Andi
-- 
ak@...ux.intel.com -- Speaking for myself only.
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