[Qemu-devel] Re: Slow PXE boot in qemu.git (fast in qemu-kvm.git)

[Anthony Liguori]

On 04/08/2011 06:25 PM, Luiz Capitulino wrote:
> Hi there,
>
> Summary:
>
>   - PXE boot in qemu.git (HEAD f124a41) is quite slow, more than 5 minutes. Got
>     the problem with e1000, virtio and rtl8139. However, pcnet *works* (it's
>     as fast as qemu-kvm.git)
>
>   - PXE boot in qemu-kvm.git (HEAD df85c051) is fast, less than a minute. Tried
>     with e1000, virtio and rtl8139 (I don't remember if I tried with pcnet)
>
> I tried with qemu.git v0.13.0 in order to check if this was a regression, but
> I got the same problem...
>
> Then I inspected qemu-kvm.git under the assumption that it could have a fix
> that wasn't commited to qemu.git. Found this:
>
>   - commit 0836b77f0f65d56d08bdeffbac25cd6d78267dc9 which is merge, works
>
>   - commit cc015e9a5dde2f03f123357fa060acbdfcd570a4 does not work (it's slow)
>
> I tried a bisect, but it brakes due to gcc4 vs. gcc3 changes. Then I inspected
> commits manually, and found out that commit 64d7e9a4 doesn't work, which makes
> me think that the fix could be in the conflict resolution of 0836b77f, which
> makes me remember that I'm late for diner, so my conclusions at this point are
> not reliable :)

Can you run kvm_stat to see what the exit rates are?

Maybe we're missing a coalesced io in qemu.git?  It's also possible that 
gpxe is hitting the apic or pit quite a lot.

Regards,

Anthony Liguori

> Ideas?
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