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

[Alex Williamson <alex.williamson@redhat.com>]

On Mon, 2011-04-11 at 22:04 +0200, 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.

I've probably been told, but forget.  Why isn't io-thread enabled by
default?  Thanks,

Alex