linux-kernel - Re: perf: more ABI breakage

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Message-ID: <20130708164721.GC22923@dyad.programming.kicks-ass.net>
Date:	Mon, 8 Jul 2013 18:47:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: perf: more ABI breakage

On Mon, Jul 08, 2013 at 11:24:18AM -0400, Vince Weaver wrote:
> 
> I guess I should have been noisier about this at the time.
> 
> Linux 3.9 came with commit
>    e259514eef764a5286873618e34c560ecb6cff13
> that enabled AMD fam15h Northbridge support, by exposing the events as 
> part of the core CPU.
> 
> Then Linux 3.10 changed this with
>    c43ca5091a374c1f6778bd7e4a39a5a10735a917
> and split them out as a separate PMU.
> 
> This of course breaks libpfm4 and thus PAPI

Urgh, so the 3.9 patches should never have been merged and sunk in while I was
doing my vegetable imitation.

Stephane agreed with the change in 3.10; and I suppose he overlooked the fact
that people were already using it :/ I specifically asked if there were already
users as that would indeed require some form of backwards compatibility --
however annoying.

But to answer your question, no we should not blindly break stuff like this --
but yeah it would have been ever so much more useful for people to report this
before we ship a release.

Stephane; do you see a sane way to bridge this now?

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