From mboxrd@z Thu Jan  1 00:00:00 1970
From: fche@redhat.com (Frank Ch. Eigler)
Subject: Re: [PATCH] KVM: Add wrapper script around QEMU to
	test kernels
Date: Mon, 07 Nov 2011 15:03:00 -0500
Message-ID: <y0mpqh3og3v.fsf@fche.csb>
References: <4EB6AE34.2000907@redhat.com>
	<CAOJsxLFGAnNL9uA=WHD8eJVs5V2+BSrtC+3ff2FsPi326dtjZw@mail.gmail.com>
	<4EB6BAED.2030400@redhat.com> <4EB6BEFA.6000303@codemonkey.ws>
	<20111106183132.GA4500@thunk.org>
	<CAOJsxLHvYo5zA+_m-AXuZHjAcGKE5q0ytmPCZ0Gye52LWq1p9Q@mail.gmail.com>
	<CAOJsxLG6kyq-RoQiBj0B_tThvOy1AxJf6XB2VfQFQJkwQ5cHcQ@mail.gmail.com>
	<20111106231953.GD4500@thunk.org>
	<alpine.LFD.2.02.1111070838520.1823@tux.localdomain>
	<alpine.DEB.2.02.1111071156230.28615@pianoman.cluster.toy>
	<20111107175942.GA9395@elte.hu>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>, Alexander Graf <agraf@suse.de>,
	Ted Ts'o <tytso@mit.edu>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
	"kvm@vger.kernel.org list" <kvm@vger.kernel.org>,
	qemu-devel Developers <qemu-devel@nongnu.org>,
	Vince Weaver <vince@deater.net>,
	"linux-kernel@vger.kernel.org List" <linux-kernel@vger.kernel.org>,
	Pekka Enberg <penberg@kernel.org>, Blue Swirl <blauwirbel@gmail.com>,
	Pekka Enberg <penberg@cs.helsinki.fi>, Avi Kivity <avi@redhat.com>,
	=?us-ascii?Q?=3D=3Fiso-8859-1=3FQ=3FAm=3DE9rico=3F=3D?= Wang
	<xiyou.wangcong@gmail.com>, Linus Torvalds <torvalds@linux-foundation.org>
To: Ingo Molnar <mingo@elte.hu>
Return-path: <qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org>
In-Reply-To: <20111107175942.GA9395@elte.hu> (Ingo Molnar's message of "Mon,
	7 Nov 2011 18:59:42 +0100")
List-Unsubscribe: <https://lists.nongnu.org/mailman/options/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>
List-Archive: <http://lists.nongnu.org/archive/html/qemu-devel>
List-Post: <mailto:qemu-devel@nongnu.org>
List-Help: <mailto:qemu-devel-request@nongnu.org?subject=help>
List-Subscribe: <https://lists.nongnu.org/mailman/listinfo/qemu-devel>,
	<mailto:qemu-devel-request@nongnu.org?subject=subscribe>
Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org
Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org
List-Id: kvm.vger.kernel.org

Ingo Molnar <mingo@elte.hu> writes:

> [...]
>> It's problem enough that there's no way to know what version of the 
>> perf_event abi you are running against and we have to guess based 
>> on kernel version.  This gets "fun" because all of the vendors have 
>> backported seemingly random chunks of perf_event code to their 
>> older kernels.
>
> The ABI design allows for that kind of flexible extensibility, and 
> it's one of its major advantages.
>
> What we *cannot* protect against is you relying on obscure details of 
> the ABI [...]

Is there some documentation that clearly spells out which parts of the
perf syscall userspace ABI are "obscure" and thus presumably
changeable?

> [...]  The usual ABI rules also apply: we'll revert everything that
> breaks the ABI - but for that you need to report it *in time* [...]

If the ABI is so great in its flexible extensibility, how come it
can't be flexibly extended without having to passing the burden of
compatibility testing & reversion-yawping to someone else?


- FChE