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

From:  Ingo Molnar <>
To:  Avi Kivity <>
Subject:  Re: [RFC] Unify KVM kernel-space and user-space code into a single project
Date:  Mon, 22 Mar 2010 12:23:40 +0100
Cc:  Anthony Liguori <>, Pekka Enberg <>, "Zhang, Yanmin" <>, Peter Zijlstra <>, Sheng Yang <>,,, Marcelo Tosatti <>, oerg Roedel <>, Jes Sorensen <>, Gleb Natapov <>, Zachary Amsden <>,, Arnaldo Carvalho de Melo <>, Fr?d?ric Weisbecker <>
Archive-link:  Article, Thread

* Avi Kivity <> 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 



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