linux-kernel - Re: [Qemu-devel] [PATCH v4 11/15] target-s390x: New QMP command query-cpu-model

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Message-ID: <20150331111043.078443f8@bee>
Date:	Tue, 31 Mar 2015 11:10:43 +0200
From:	Michael Mueller <mimu@...ux.vnet.ibm.com>
To:	Eduardo Habkost <ehabkost@...hat.com>
Cc:	linux-s390@...r.kernel.org, kvm@...r.kernel.org,
	Gleb Natapov <gleb@...nel.org>, linux-kernel@...r.kernel.org,
	Alexander Graf <agraf@...e.de>, qemu-devel@...gnu.org,
	Christian Borntraeger <borntraeger@...ibm.com>,
	Daniel Hansel <daniel.hansel@...ux.vnet.ibm.com>,
	"Jason J. Herne" <jjherne@...ux.vnet.ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Andreas Faerber <afaerber@...e.de>,
	Richard Henderson <rth@...ddle.net>
Subject: Re: [Qemu-devel] [PATCH v4 11/15] target-s390x: New QMP command
 query-cpu-model

On Mon, 30 Mar 2015 16:50:20 -0300
Eduardo Habkost <ehabkost@...hat.com> wrote:

Hello Eduardo,

> On Mon, Mar 30, 2015 at 04:28:24PM +0200, Michael Mueller wrote:
> [...]
> > diff --git a/target-s390x/cpu.c b/target-s390x/cpu.c
> > index 829945d..1698b52 100644
> > --- a/target-s390x/cpu.c
> > +++ b/target-s390x/cpu.c
> > @@ -37,6 +37,11 @@
> >  #define CR0_RESET       0xE0UL
> >  #define CR14_RESET      0xC2000000UL;
> >  
> > +static inline char *strdup_s390_cpu_name(S390CPUClass *cc)
> > +{
> > +    return g_strdup_printf("%04x-ga%u", cc->proc.type, cc->mach.ga);
> > +}
> > +
> >  /* generate CPU information for cpu -? */
> >  void s390_cpu_list(FILE *f, fprintf_function cpu_fprintf)
> >  {
> > @@ -74,6 +79,30 @@ CpuDefinitionInfoList *arch_query_cpu_definitions(Error **errp)
> >  
> >      return entry;
> >  }
> > +
> > +CpuModelInfo *arch_query_cpu_model(Error **errp)
> > +{
> > +    CpuModelInfo *info;
> > +    S390CPUClass *cc;
> > +
> > +    if (!s390_cpu_models_used()) {
> > +        return NULL;
> > +    }
> 
> First question is: why you don't want to just return
>   { name: "none", accel: ...  }
> when TYPE_S390_CPU ("-cpu none") is used?

That's a good idea, indeed! CPU model "none" is used as well in case option -cpu is omitted.

> 
> Now, assuming that you really want to return NULL if -cpu none is used,
> why don't you just ask for the first CPU (like you already do below) and
> check if it is a named CPU model, instead of adding a new global? e.g.:
> 
>     static bool s390_cpu_class_is_model(S390CPUClass *cc)
>     {
>         return cpuid(cc->proc) != 0;
>     }
>     
>     CpuModelInfo *arch_query_cpu_model(Error **errp)
>     {
>         S390CPUClass *cc;
>         S390CPUClass *cc;
> 
>         cc = S390_CPU_GET_CLASS(s390_cpu_addr2state(0));
>         if (!s390_cpu_class_is_model(cc)) {
>             return NULL;
>         }
>         [...]
>     }
> 
> 
> > +    info = g_try_new0(CpuModelInfo, 1);
> > +    if (!info) {
> > +        return NULL;
> > +    }
> > +    cc = S390_CPU_GET_CLASS(s390_cpu_addr2state(0));
> > +    info->name = strdup_s390_cpu_name(cc);
> 
> I don't think the current version of strdup_s390_cpu_name() can ever
> return NULL. Do you expect it to return NULL in the future?

No I do not expect this. I will drop the NULL test.

> 
> > +    if (!info->name) {
> > +        g_free(info);
> > +        return NULL;
> > +    }
> > +    if (kvm_enabled()) {
> > +        info->accel = ACCEL_ID_KVM;
> 
> This could be a CPUState field, added automatically by
> cpu_generic_init() using current_machine->accel.

I will add a CPUState field and see how it works out...

> 
> > +    }
> > +    return info;
> > +}
> >  #endif
> >  
> >  static void s390_cpu_set_pc(CPUState *cs, vaddr value)
> > -- 
> > 1.8.3.1
> > 
> 

Thanks a lot,
Michael

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