Re: [Qemu-devel] [PATCH 18/19] target-ppc: Enhance the CPU node labels for the guest device tree for pseries.

[Andreas Färber]

Hi,

Am 08.07.2013 17:49, schrieb Prerna Saxena:
> On 07/08/2013 02:32 PM, Andreas Färber wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> Am 08.07.2013 03:09, schrieb David Gibson:
>>> On Sat, Jul 06, 2013 at 11:54:15PM +1000, Alexey Kardashevskiy
>>> wrote:
>>>> @@ -1342,6 +1346,13 @@ static void
>>>> ppc_spapr_init(QEMUMachineInitArgs *args) 
>>>> register_savevm_live(NULL, "spapr/htab", -1, 1, 
>>>> &savevm_htab_handlers, spapr);
>>>>
>>>> +    /* Ensure that cpu_model is correctly reflected for a KVM
>>>> guest */ +    if (kvm_enabled() && !strcmp(cpu_model, "host")) { 
>>>> +        asm ("mfpvr %0" +            : "=r"(pvr)); +
>>>> cpu_model = ppc_cpu_alias_by_pvr(pvr);
>>>
>>> This needs to be protected by an ifdef CONFIG_KVM or similar.  If
>>> the compiler optimization level is turned down, so that it doesn't 
>>> recognize that the kvm_enabled() is always false, then this could 
>>> attempt to compile the ppc asm instructions on an x86 (or
>>> whatever) host.
>>
>> This hunk can be completely replaced by QOM mechanisms - just didn't
>> get to replying yet...
> 
> Sorry I already sent out a v2, and only then saw your message. Could you
> pls explain how I could use QOM to replace this code block ?

Well, in short the thing is it has not much to do with KVM. The
KVM-specific host-powerpc64-cpu type is derived from the one you're
looking for and thus you can use object_class_get_parent() to obtain the
parent type and look at its name - stripping "-" TYPE_POWERPC_CPU from
it should be much more efficient but will give you the detailed name
including revision. I was planning to propose an alternative patch for that.

Replacing a concrete model name with its simpler alias is a secondary
issue (separate patch) that is not specific to KVM or -cpu host. Compare
-cpu POWER8_v1.0 printing .../address@hidden/... presumably.

Further, Alex has already applied a patch of his working around the
alias table being a rather archaic construct, not intended for frequent
use. Instead of adding even more functions that iterate it, we should
turn it into a hashtable for efficient lookup.

(Note that the cpu_model_str field may contain more than just the model
name, it is otherwise unused in softmmu and I was therefore preparing a
patch to ban its use to linux-user solely, so the type name seems the
most reliable indicator we have and as a bonus no PVR needed for it.)

Regards,
Andreas

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