linux-kernel - Re: [RFC] Unify KVM kernel-space and user-space code into a single project

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Message-ID: <20100322112340.GD3483@elte.hu>
Date:	Mon, 22 Mar 2010 12:23:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Avi Kivity <avi@...hat.com>
Cc:	Anthony Liguori <anthony@...emonkey.ws>,
	Pekka Enberg <penberg@...helsinki.fi>,
	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Sheng Yang <sheng@...ux.intel.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Marcelo Tosatti <mtosatti@...hat.com>,
	oerg Roedel <joro@...tes.org>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	Gleb Natapov <gleb@...hat.com>,
	Zachary Amsden <zamsden@...hat.com>, ziteng.huang@...el.com,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	Fr?d?ric Weisbecker <fweisbec@...il.com>
Subject: Re: [RFC] Unify KVM kernel-space and user-space code into a single
 project

* Avi Kivity <avi@...hat.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
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