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Date: Fri, 3 Jun 2016 11:37:49 +0200
From: Igor Mammedov <imammedo@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH RFC 4/8] target-i386: cpu: consolidate
 calls of object_property_parse() in x86_cpu_parse_featurestr
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To: Peter Krempa <pkrempa@redhat.com>
Cc: peter.maydell@linaro.org, Eduardo Habkost <ehabkost@redhat.com>, libvir-list@redhat.com, mark.cave-ayland@ilande.co.uk, qemu-devel@nongnu.org, blauwirbel@gmail.com, qemu-arm@nongnu.org, pbonzini@redhat.com, Jiri Denemark <jdenemar@redhat.com>, rth@twiddle.net

On Fri, 3 Jun 2016 09:30:09 +0200
Peter Krempa <pkrempa@redhat.com> wrote:

> On Thu, Jun 02, 2016 at 18:31:04 +0200, Igor Mammedov wrote:
> > On Thu, 2 Jun 2016 17:05:06 +0200
> > Peter Krempa <pkrempa@redhat.com> wrote:  
> > > On Thu, Jun 02, 2016 at 11:53:22 -0300, Eduardo Habkost wrote:  
> > > > On Thu, Jun 02, 2016 at 02:22:22PM +0200, Igor Mammedov wrote:  
> 
> [...]
> 
> > > I couldn't find anything regarding xlevel (so we might actually not
> > > support it at all), but we indeed do limit the hv_spinlock count:
> > > 
> > > 
> > >                 if (def->hyperv_spinlocks < 0xFFF) {
> > >                     virReportError(VIR_ERR_XML_ERROR, "%s",
> > >                                    _("HyperV spinlock retry count must be "
> > >                                      "at least 4095"));
> > >                     goto error;
> > >                 }
> > > 
> > > Peter  
> > Peter,
> > Does libvirt still uses -cpu xxx,+feat1,-feat2 syntax
> > or canonical property syntax there feat1=on,feat2=off  
> 
> We use the legacy one:
> 
> -cpu core2duo,+ds,+acpi,+ht,+tm,+ds_cpl, ...
> 
> and
> 
> -cpu 'qemu32,hv_relaxed,hv_vapic, ... 
> 
> for the hyperv features.
> 
> We probably can switch to the new one if there's a reasonable way how to
> detect that qemu is supporting the new one.
for x86 features became properties since 2.4 release (commit 38e5c119),
that's the one way to know it.
But it's still only +-features for sparc (that's the last remaining
target that has legacy parsing).

Another way to detect it is to probe via QOM if CPU has a property corresponding
to a feature.

Maybe Eduardo knows about other ways to do it.

> 
> Peter
>