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

Avi Kivity
2010-03-18T13:46:06Z

On 03/18/2010 03:31 PM, Ingo Molnar wrote:
> * Avi Kivity<avi@redhat.com> wrote:
>
>
>> On 03/18/2010 03:02 PM, Ingo Molnar wrote:
>>
>>>
>>>> [...] What users eagerly replace their kernels?
>>>>
>>> Those 99% who click on the 'install 193 updates' popup.
>>>
>>>
>> Of which 1 is the kernel, and 192 are userspace updates (of which one may be
>> qemu).
>>
> I think you didnt understand my (tersely explained) point - which is probably
> my fault. What i said is:
>
> - distros update the kernel first. Often in stable releases as well if
> there's a new kernel released. (They must because it provides new hardware
> enablement and other critical changes they generally cannot skip.)
>

No, they don't. RHEL 5 is still on 2.6.18, for example. Users don't
like their kernels updated unless absolutely necessary, with good reason.

Kernel updates = reboots.

> - Qemu on the other hand is not upgraded with (nearly) that level of urgency.
> Completely new versions will generally have to wait for the next distro
> release.
>

F12 recently updated to 2.6.32. This is probably due to 2.6.31.stable
dropping away, and no capacity at Fedora to maintain it on their own.
So they are caught in a bind - stay on 2.6.31 and expose users to
security vulnerabilities or move to 2.6.32 and cause regressions. Not a
happy choice.

> With in-kernel tools the kernel and the tooling that accompanies the kernel
> are upgraded in the same low-latency pathway. That is a big plus if you are
> offering things like instrumentation (which perf does), which relates closely
> to the kernel.
>
> Furthermore, many distros package up the latest -git kernel as well. They
> almost never do that with user-space packages.
>

I'm sure if we ask the Fedora qemu maintainer to package qemu-kvm.git
they'll consider it favourably. Isn't that what rawhide is for?

> Let me give you a specific example:
>
> I'm running Fedora Rawhide with 2.6.34-rc1 right now on my main desktop, and
> that comes with perf-2.6.34-0.10.rc1.git0.fc14.noarch.
>
> My rawhide box has qemu-kvm-0.12.3-3.fc14.x86_64 installed. That's more than a
> 1000 Qemu commits older than the latest Qemu development branch.
>
> So by being part of the kernel repo there's lower latency upgrades and earlier
> and better testing available on most distros.
>
> You made it very clear that you dont want that, but please dont try to claim
> that those advantages do not exist - they are very much real and we are making
> good use of it.
>

I don't mind at all if rawhide users run on the latest and greatest, but
release users deserve a little more stability.

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