Re: [Adeos-main] Reworking ipipe timer subsystem,

[Jan Kiszka <jan.kiszka@domain.hid>]

On 2012-04-03 13:06, Gilles Chanteperdrix wrote:
> On 04/03/2012 09:59 AM, Jan Kiszka wrote:
>> On 2012-04-03 09:54, Gilles Chanteperdrix wrote:
>>> On 04/02/2012 11:58 PM, Jan Kiszka wrote:
>>>> On 2012-04-02 23:55, Gilles Chanteperdrix wrote:
>>>>> On 04/02/2012 10:59 PM, Jan Kiszka wrote:
>>>>>> On 2012-04-02 22:56, Jan Kiszka wrote:
>>>>>>>> No luck, I am using qemu 0.12.5, there is no -global option documented,
>>>>>>>
>>>>>>> Err, that's prehistoric. Use stable 1.0.x at least to receive proper
>>>>>>> HPET support.
>>>>>>
>>>>>> Oh, and there is one further pitfall: You need to provide
>>>>>> -no-kvm-irqchip to use the HPET with MSI support because qemu-kvm does
>>>>>> not forward those MSIs to the kernel irqchip model. I'm sitting on
>>>>>> patches...
>>>>>
>>>>> Yes, I needed that. It works now, except that I could not find how to
>>>>> use an NFS root filesystem. But with an ext3 file-backed filesystem, I
>>>>> could get that:
>>>>
>>>> If your NFS server runs on the host and you use userspace networking
>>>> (default without additional parameters), the guest should be able to
>>>> reach the server under 10.0.2.2 and use an IP like 10.0.2.15 (or dhcp).
>>>> However, I recently failed to get this working as well but didn't dig
>>>> deeper.
>>>
>>> Well, with -net user, I do not get any network interface on the
>>> simulated kernel. Maybe there a special network driver to enable in the
>>> kernel? The documentation does not say which network card is simulated,
>>> and I do not see any with lspci.
>>
>> qemu-kvm emulates a rtl8139 by default. But, by just specifying -net
>> user, you disable any network adapter. Just leave it out, -net user -net
>> nic,model=rtl8139 is default.
> 
> How is -net user supposed to work if there is no emulated nic on the
> board. I tried -net nic first, but it did not work either, it seems to
> use vlans, but I do not have vlans configured on my host nor any desire
> to configure them. Is there not a way to simply share the host network
> interface with the guest, the way virtualbox does it?

QEMU vlans have nothing to do with vlan frames on the wire.

Just leave out any -net command line switch and you will get a 8139
attached to a userspace networking stack out of the box.

> 
>>
>>>
>>> Something else, is it possible to run kvm using SCHED_FIFO policy? I
>>> tried that and I almost got a lockup, was probably saved by throttling.
>>
>> Yes, but not without some patches and a lot of tuning on both guest and
>> host side. A standard Linux kernel touches too many device models that
>> will take a long time to make RT compatible. A simple access to a
>> virtual graphic adapter will be like accessing a screwed up physical GPU
>> with horrible latency.
> 
> Yes, ok, but my main interest was the timer interrupt. Besides this does
> not explain why I get a lockup.

E.g. because the guest may spin in its VCPU thread waiting for events
that the IO thread of QEMU cannot deliver as it gets no CPU time.

Jan

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