Re: Slow PXE boot in qemu.git (fast in qemu-kvm.git)

[Anthony Liguori <anthony@codemonkey.ws>]

On 04/11/2011 03:04 PM, Jan Kiszka 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?
>
>> So, does this have to be fixed w/o I/O thread?
> If it's most probably an architectural deficit of non-io-thread mode, I
> would say let it rest in peace. But maybe it points to a generic issues
> that is just magnified by non-threaded mode.

If gpxe is spinning waiting for I/O to complete, that's going to prevent 
select from running until the next signal (timer event).

Regards,

Anthony Liguori

> Jan
>