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

[Jan Kiszka <jan.kiszka@web.de>]

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On 2011-04-11 23:05, Luiz Capitulino wrote:
> On Mon, 11 Apr 2011 22:04:52 +0200
> Jan Kiszka <jan.kiszka@web.de> wrote:
> 
>> On 2011-04-11 21:15, Luiz Capitulino wrote:
>>> On Mon, 11 Apr 2011 13:00:32 -0600
>>> Alex Williamson <alex.williamson@redhat.com> wrote:
>>>
>>>> On Mon, 2011-04-11 at 15:35 -0300, Luiz Capitulino wrote:
>>>>> On Fri, 08 Apr 2011 19:50:57 -0500
>>>>> Anthony Liguori <anthony@codemonkey.ws> wrote:
>>>>>
>>>>>> 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 was having this problem too, but I think it's because I forgot to
>>>> build qemu with --enable-io-thread, which is the default for qemu-kvm.
>>>> Can you re-configure and build with that and see if it's fast?  Thanks,
>>>
>>> Yes, nice catch, it's faster with I/O thread enabled, even seem faster
>>> than qemu-kvm.git.
>>
>> What's the performance under qemu-kvm with -no-kvm-irqchip?
> 
> Still fast, 

I meant: is it even faster with unaccelerated userspace irqchip? I've
seen such effects with emulated NICs before.

> but just realized that qemu-kvm's configure says that I/O thread
> is disabled:
> 
>  IO thread         no
> 
> And it's fast..

That only means (so far) that the upstream io-thread code is disabled.
Qemu-kvm's own solution is enabled all the time, and you can't switch to
upstream anyway as both are incompatible. That's going to change soon
(hopefully) when we migrate qemu-kvm to the upstream version.

Jan


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