From mboxrd@z Thu Jan  1 00:00:00 1970
From: Ingo Molnar <mingo@elte.hu>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project
Date: Mon, 22 Mar 2010 12:23:40 +0100
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Cc: Anthony Liguori <anthony@codemonkey.ws>,
	Pekka Enberg <penberg@cs.helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@linux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Sheng Yang <sheng@linux.intel.com>,
	linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Marcelo Tosatti <mtosatti@redhat.com>,
	oerg Roedel <joro@8bytes.org>,
	Jes Sorensen <Jes.Sorensen@redhat.com>,
	Gleb Natapov <gleb@redhat.com>,
	Zachary Amsden <zamsden@redhat.com>, ziteng.huang@intel.com,
	Arnaldo Carvalho de Melo <acme@redhat.com>,
	Fr?d?ric Weisbecker <fweisbec@gmail.com>
To: Avi Kivity <avi@redhat.com>
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* Avi Kivity <avi@redhat.com> wrote:

> IMO the reason perf is more usable than oprofile has less to do with the 
> kernel/userspace boundary and more do to with effort and attention spent on 
> the userspace/user boundary.
>
> [...]

If you are interested in the first-hand experience of the people who are doing 
the perf work then here it is: by far the biggest reason for perf success and 
perf usability is the integration of the user-space tooling with the 
kernel-space bits, into a single repository and project.

The very move you are opposing so vehemently for KVM.

Oprofile went the way you proposed, and it was a failure. It failed not 
because it was bad technology (it was pretty decent and people used it), it 
was not a failure because the wrong people worked on it (to the contrary, very 
capable people worked on it), it was a failure in hindsight because it simply 
incorrectly split into two projects which stiffled the progress of each other.

Obviously 3 years ago you'd have seen a similar, big "Oprofile is NOT broken!" 
flamewar, had i posted the same observations about Oprofile that i expressed 
about KVM here. (In fact there was a similar, big flamewar about all this when 
perf was posted a year ago.)

And yes, (as you are aware of) i see very similar patterns of inefficiency in 
the KVM/Qemu tooling relationship as well, hence did i express my views about 
it.

Thanks,

	Ingo