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


From: Anthony Liguori
Subject: Re: [Qemu-devel] Slow PXE boot in qemu.git (fast in qemu-kvm.git)
Date: Mon, 11 Apr 2011 19:39:44 -0500
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.15) Gecko/20110411 Lightning/1.0b2 Thunderbird/3.1.9

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<address@hidden>  wrote:

On Mon, 2011-04-11 at 15:35 -0300, Luiz Capitulino wrote:
On Fri, 08 Apr 2011 19:50:57 -0500
Anthony Liguori<address@hidden>  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





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