qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

[libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Collin Walling 5 years, 9 months ago

Use model name "qemu" instead of "max" when calling
query-cpu-model-expansion for s390 on tcg.

Signed-off-by: Collin Walling <walling@linux.ibm.com>
---
 src/qemu/qemu_capabilities.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 23b4833..e9b44cc 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
 
     if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
         virtType = VIR_DOMAIN_VIRT_QEMU;
-        model = "max";
+        if (ARCH_IS_S390(qemuCaps->arch))
+            model = "qemu";
+        else
+            model = "max";
     } else {
         virtType = VIR_DOMAIN_VIRT_KVM;
         model = "host";
-- 
2.7.4

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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Jiri Denemark 5 years, 9 months ago

On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
> Use model name "qemu" instead of "max" when calling
> query-cpu-model-expansion for s390 on tcg.
> 
> Signed-off-by: Collin Walling <walling@linux.ibm.com>
> ---
>  src/qemu/qemu_capabilities.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> index 23b4833..e9b44cc 100644
> --- a/src/qemu/qemu_capabilities.c
> +++ b/src/qemu/qemu_capabilities.c
> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
>  
>      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>          virtType = VIR_DOMAIN_VIRT_QEMU;
> -        model = "max";
> +        if (ARCH_IS_S390(qemuCaps->arch))
> +            model = "qemu";
> +        else
> +            model = "max";

I think we should also check if "max" is a supported model
(qemuCaps->tcgCPUModels is already populated at this point) and only use
"qemu" on s390 if "max" is not supported. And please, report the issue
to QEMU developers since one of the reasons behind "max" is its
universal availability on everywhere CPU model expansion is supported.

Jirka

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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Cornelia Huck 5 years, 9 months ago

On Tue, 24 Jul 2018 18:08:21 +0200
Jiri Denemark <jdenemar@redhat.com> wrote:

> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
> > Use model name "qemu" instead of "max" when calling
> > query-cpu-model-expansion for s390 on tcg.
> > 
> > Signed-off-by: Collin Walling <walling@linux.ibm.com>
> > ---
> >  src/qemu/qemu_capabilities.c | 5 ++++-
> >  1 file changed, 4 insertions(+), 1 deletion(-)
> > 
> > diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> > index 23b4833..e9b44cc 100644
> > --- a/src/qemu/qemu_capabilities.c
> > +++ b/src/qemu/qemu_capabilities.c
> > @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
> >  
> >      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
> >          virtType = VIR_DOMAIN_VIRT_QEMU;
> > -        model = "max";
> > +        if (ARCH_IS_S390(qemuCaps->arch))
> > +            model = "qemu";
> > +        else
> > +            model = "max";  
> 
> I think we should also check if "max" is a supported model
> (qemuCaps->tcgCPUModels is already populated at this point) and only use
> "qemu" on s390 if "max" is not supported. And please, report the issue
> to QEMU developers since one of the reasons behind "max" is its
> universal availability on everywhere CPU model expansion is supported.

Hm, can you point me to that discussion? A quick search through the
QEMU log gives me the addition of the "max" model on i386 as a
replacement to the "host" model for !kvm, but nothing about it being
universal...

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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Daniel P. Berrangé 5 years, 9 months ago

On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote:
> On Tue, 24 Jul 2018 18:08:21 +0200
> Jiri Denemark <jdenemar@redhat.com> wrote:
> 
> > On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
> > > Use model name "qemu" instead of "max" when calling
> > > query-cpu-model-expansion for s390 on tcg.
> > > 
> > > Signed-off-by: Collin Walling <walling@linux.ibm.com>
> > > ---
> > >  src/qemu/qemu_capabilities.c | 5 ++++-
> > >  1 file changed, 4 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
> > > index 23b4833..e9b44cc 100644
> > > --- a/src/qemu/qemu_capabilities.c
> > > +++ b/src/qemu/qemu_capabilities.c
> > > @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
> > >  
> > >      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
> > >          virtType = VIR_DOMAIN_VIRT_QEMU;
> > > -        model = "max";
> > > +        if (ARCH_IS_S390(qemuCaps->arch))
> > > +            model = "qemu";
> > > +        else
> > > +            model = "max";  
> > 
> > I think we should also check if "max" is a supported model
> > (qemuCaps->tcgCPUModels is already populated at this point) and only use
> > "qemu" on s390 if "max" is not supported. And please, report the issue
> > to QEMU developers since one of the reasons behind "max" is its
> > universal availability on everywhere CPU model expansion is supported.
> 
> Hm, can you point me to that discussion? A quick search through the
> QEMU log gives me the addition of the "max" model on i386 as a
> replacement to the "host" model for !kvm, but nothing about it being
> universal...

I don't recall the link but "max" is supposed to be the standard shorthand
for "enable all the features supported by the virt type". IOW, 'max' should
work both KVM and TCG ("host" was only well defined for KVM), and across
all architectures.

So having to use a different name on s390 is a bug in QEMU imho.

Regards,
Daniel
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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by David Hildenbrand 5 years, 9 months ago

On 24.07.2018 18:59, Daniel P. Berrangé wrote:
> On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote:
>> On Tue, 24 Jul 2018 18:08:21 +0200
>> Jiri Denemark <jdenemar@redhat.com> wrote:
>>
>>> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
>>>> Use model name "qemu" instead of "max" when calling
>>>> query-cpu-model-expansion for s390 on tcg.
>>>>
>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>> ---
>>>>  src/qemu/qemu_capabilities.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>>>> index 23b4833..e9b44cc 100644
>>>> --- a/src/qemu/qemu_capabilities.c
>>>> +++ b/src/qemu/qemu_capabilities.c
>>>> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
>>>>  
>>>>      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>>>>          virtType = VIR_DOMAIN_VIRT_QEMU;
>>>> -        model = "max";
>>>> +        if (ARCH_IS_S390(qemuCaps->arch))
>>>> +            model = "qemu";
>>>> +        else
>>>> +            model = "max";  
>>>
>>> I think we should also check if "max" is a supported model
>>> (qemuCaps->tcgCPUModels is already populated at this point) and only use
>>> "qemu" on s390 if "max" is not supported. And please, report the issue
>>> to QEMU developers since one of the reasons behind "max" is its
>>> universal availability on everywhere CPU model expansion is supported.
>>
>> Hm, can you point me to that discussion? A quick search through the
>> QEMU log gives me the addition of the "max" model on i386 as a
>> replacement to the "host" model for !kvm, but nothing about it being
>> universal...
> 
> I don't recall the link but "max" is supposed to be the standard shorthand
> for "enable all the features supported by the virt type". IOW, 'max' should
> work both KVM and TCG ("host" was only well defined for KVM), and across
> all architectures.

I remember the discussions and I agreed back than that this was the
right thing to do.

Looks like x86, arm and ppc have it. We should have it, too.

> 
> So having to use a different name on s390 is a bug in QEMU imho.
> 

While this should be fixed, it is compat handling and not really a BUG.

> Regards,
> Daniel
> 


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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Collin Walling 5 years, 9 months ago

On 07/24/2018 12:59 PM, Daniel P. Berrangé wrote:
> On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote:
>> On Tue, 24 Jul 2018 18:08:21 +0200
>> Jiri Denemark <jdenemar@redhat.com> wrote:
>>
>>> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
>>>> Use model name "qemu" instead of "max" when calling
>>>> query-cpu-model-expansion for s390 on tcg.
>>>>
>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>> ---
>>>>  src/qemu/qemu_capabilities.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>>>> index 23b4833..e9b44cc 100644
>>>> --- a/src/qemu/qemu_capabilities.c
>>>> +++ b/src/qemu/qemu_capabilities.c
>>>> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
>>>>  
>>>>      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>>>>          virtType = VIR_DOMAIN_VIRT_QEMU;
>>>> -        model = "max";
>>>> +        if (ARCH_IS_S390(qemuCaps->arch))
>>>> +            model = "qemu";
>>>> +        else
>>>> +            model = "max";  
>>>
>>> I think we should also check if "max" is a supported model
>>> (qemuCaps->tcgCPUModels is already populated at this point) and only use
>>> "qemu" on s390 if "max" is not supported. And please, report the issue
>>> to QEMU developers since one of the reasons behind "max" is its
>>> universal availability on everywhere CPU model expansion is supported.
>>
>> Hm, can you point me to that discussion? A quick search through the
>> QEMU log gives me the addition of the "max" model on i386 as a
>> replacement to the "host" model for !kvm, but nothing about it being
>> universal...
> 
> I don't recall the link but "max" is supposed to be the standard shorthand
> for "enable all the features supported by the virt type". IOW, 'max' should
> work both KVM and TCG ("host" was only well defined for KVM), and across
> all architectures.
> 
> So having to use a different name on s390 is a bug in QEMU imho.
> 
> Regards,
> Daniel
> 

Thanks for expanding on what the "max" model name is suppose to be. I wonder if a 
s/"qemu"/"max" in QEMU would suffice (I'm taking a shot in the dark here.)

@Connie, @David, you both are far more knowledgeable in this area than I am. What
do either of you suggest for moving forward with this? Should we forward this
discussion on qemu-devel?

-- 
Respectfully,
- Collin Walling

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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by David Hildenbrand 5 years, 9 months ago

On 25.07.2018 01:02, Collin Walling wrote:
> On 07/24/2018 12:59 PM, Daniel P. Berrangé wrote:
>> On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote:
>>> On Tue, 24 Jul 2018 18:08:21 +0200
>>> Jiri Denemark <jdenemar@redhat.com> wrote:
>>>
>>>> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
>>>>> Use model name "qemu" instead of "max" when calling
>>>>> query-cpu-model-expansion for s390 on tcg.
>>>>>
>>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>>> ---
>>>>>  src/qemu/qemu_capabilities.c | 5 ++++-
>>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>>>>> index 23b4833..e9b44cc 100644
>>>>> --- a/src/qemu/qemu_capabilities.c
>>>>> +++ b/src/qemu/qemu_capabilities.c
>>>>> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
>>>>>  
>>>>>      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>>>>>          virtType = VIR_DOMAIN_VIRT_QEMU;
>>>>> -        model = "max";
>>>>> +        if (ARCH_IS_S390(qemuCaps->arch))
>>>>> +            model = "qemu";
>>>>> +        else
>>>>> +            model = "max";  
>>>>
>>>> I think we should also check if "max" is a supported model
>>>> (qemuCaps->tcgCPUModels is already populated at this point) and only use
>>>> "qemu" on s390 if "max" is not supported. And please, report the issue
>>>> to QEMU developers since one of the reasons behind "max" is its
>>>> universal availability on everywhere CPU model expansion is supported.
>>>
>>> Hm, can you point me to that discussion? A quick search through the
>>> QEMU log gives me the addition of the "max" model on i386 as a
>>> replacement to the "host" model for !kvm, but nothing about it being
>>> universal...
>>
>> I don't recall the link but "max" is supposed to be the standard shorthand
>> for "enable all the features supported by the virt type". IOW, 'max' should
>> work both KVM and TCG ("host" was only well defined for KVM), and across
>> all architectures.
>>
>> So having to use a different name on s390 is a bug in QEMU imho.
>>
>> Regards,
>> Daniel
>>
> 
> Thanks for expanding on what the "max" model name is suppose to be. I wonder if a 
> s/"qemu"/"max" in QEMU would suffice (I'm taking a shot in the dark here.)

Nope, it dynamically has to map to qemu/host depending on the
accelerator. But it also has to be a valid QOM object ("max-s390x-cpu").

> 
> @Connie, @David, you both are far more knowledgeable in this area than I am. What
> do either of you suggest for moving forward with this? Should we forward this
> discussion on qemu-devel?
> 

I can have a look if nobody else wants to tackle it.


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Re: [libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

Posted by Cornelia Huck 5 years, 9 months ago

On Wed, 25 Jul 2018 09:34:08 +0200
David Hildenbrand <david@redhat.com> wrote:

> On 25.07.2018 01:02, Collin Walling wrote:
> > Thanks for expanding on what the "max" model name is suppose to be. I wonder if a 
> > s/"qemu"/"max" in QEMU would suffice (I'm taking a shot in the dark here.)  
> 
> Nope, it dynamically has to map to qemu/host depending on the
> accelerator. But it also has to be a valid QOM object ("max-s390x-cpu").
> 
> > 
> > @Connie, @David, you both are far more knowledgeable in this area than I am. What
> > do either of you suggest for moving forward with this? Should we forward this
> > discussion on qemu-devel?
> >   
> 
> I can have a look if nobody else wants to tackle it.

I'll gladly merge a patch :)

This is probably 3.1 material, so libvirt will need compat handling for
it, I guess.

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