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

[Blue Swirl <blauwirbel@gmail.com>]

On Sat, Apr 9, 2011 at 2:25 AM, Luiz Capitulino <lcapitulino@redhat.com> 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 :)
>
> Ideas?

What is the test case? I tried PXE booting a 10M file with and without
KVM and the results are pretty much the same with pcnet and e1000.
time qemu -monitor stdio -boot n -net nic,model=e1000 -net
user,tftp=.,bootfile=10M -net dump,file=foo -enable-kvm
time qemu -monitor stdio -boot n -net nic,model=pcnet -net
user,tftp=.,bootfile=10M -net dump,file=foo -enable-kvm
time qemu -monitor stdio -boot n -net nic,model=e1000 -net
user,tftp=.,bootfile=10M -net dump,file=foo
time qemu -monitor stdio -boot n -net nic,model=pcnet -net
user,tftp=.,bootfile=10M -net dump,file=foo

All times are ~10s.