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Re: [libvirt] [Qemu-devel] [QEMU PATCH 3/3] x86: pc: versioned CPU model names & compatibility aliases



Am 26.07.2012 16:24, schrieb Eduardo Habkost:
> On Thu, Jul 26, 2012 at 12:52:33AM +0200, Andreas Färber wrote:
>> Am 25.07.2012 20:18, schrieb Eduardo Habkost:
>>> This adds version number to CPU model names on the "pc-<version>"
>>> machine-types, so we can create new models with bug fixes while keeping
>>> compatibility when using older machine-types.
>>>
>>> When naming the existing models, I used the last QEMU version where the
>>> model was changed (see summary below), but by coincidence every single
>>> one was changed on QEMU-1.1.
>>>
>>> - Conroe, Penryn, Nehalem, Opteron_G1, Opteron_G2, Opteron_G3:
>>>   added on 0.13, changed on 1.1
>>> - Westmere, SandyBridge, Opteron_G4: added on 1.1
>>>
>>> Signed-off-by: Eduardo Habkost <ehabkost redhat com>
>>> ---
>>>  hw/pc_piix.c                       |   56 ++++++++++++++++++++++++++++++++++++
>>>  sysconfigs/target/cpus-x86_64.conf |   18 ++++++------
>>>  2 files changed, 65 insertions(+), 9 deletions(-)
>>>
>>> diff --git a/hw/pc_piix.c b/hw/pc_piix.c
>>> index 0c0096f..ef3840f 100644
>>> --- a/hw/pc_piix.c
>>> +++ b/hw/pc_piix.c
>>> @@ -349,6 +349,18 @@ static void pc_xen_hvm_init(ram_addr_t ram_size,
>>>  }
>>>  #endif
>>>  
>>> +/* CPU aliases for pre-1.2 CPU models */
>>> +#define V1_1_CPU_ALIASES  \
>>> +    { "Conroe",      "Conroe-1.1" }, \
>>> +    { "Penryn",      "Penryn-1.1" }, \
>>> +    { "Nehalem",     "Nehalem-1.1" }, \
>>> +    { "Westmere",    "Westmere-1.1" }, \
>>> +    { "SandyBridge", "SandyBridge-1.1" }, \
>>> +    { "Opteron_G1",  "Opteron_G1-1.1" }, \
>>> +    { "Opteron_G2",  "Opteron_G2-1.1" }, \
>>> +    { "Opteron_G3",  "Opteron_G3-1.1" }, \
>>> +    { "Opteron_G4",  "Opteron_G4-1.1" },
>>> +
>>>  static QEMUMachine pc_machine_v1_2 = {
>>>      .name = "pc-1.2",
>>>      .alias = "pc",
>>> @@ -356,6 +368,10 @@ static QEMUMachine pc_machine_v1_2 = {
>>>      .init = pc_init_pci,
>>>      .max_cpus = 255,
>>>      .is_default = 1,
>>> +    .cpu_aliases = (CPUModelAlias[]) {
>>> +        V1_1_CPU_ALIASES
>>> +        {NULL, NULL},
>>> +    },
>>>  };
>>>  
>>>  #define PC_COMPAT_1_1 \
>> [...]
>>> diff --git a/sysconfigs/target/cpus-x86_64.conf b/sysconfigs/target/cpus-x86_64.conf
>>> index cee0ea9..14c7891 100644
>>> --- a/sysconfigs/target/cpus-x86_64.conf
>>> +++ b/sysconfigs/target/cpus-x86_64.conf
>>> @@ -1,7 +1,7 @@
>>>  # x86 CPU MODELS
>>>  
>>>  [cpudef]
>>> -   name = "Conroe"
>>> +   name = "Conroe-1.1"
>>>     level = "2"
>>>     vendor = "GenuineIntel"
>>>     family = "6"
>> [snip]
>>
>> So where are the actual differences between, e.g., Conroe-1.1 and
>> Conroe? I'd expect we need either an additional string applying
>> parameter presets such as maybe "x2apic=off" or a nested list of
>> (property, value) pairs.
> 
> There are no differences yet, until we make updates in the Conroe model.
> If we have to make any change (to fix a bug, for example), we would
> create a "Conroe-1.2" CPU model, and make the "pc-1.2" machine-type
> alias "Conroe" to "Conroe-1.2" while keeping the older machine-types
> using "Conroe-1.1".
> 
>>
>> As long as there's no concept for actually modelling versioned CPUs, I
>> consider this RFC stage and not worth merging yet...
> 
> What do you mean by "no concept for actually modelling versioned CPUs"?
> You mean there's no use-case or reason for versioning them, or that the
> series don't model the versioning properly?

I mean, you add infrastructure for remapping Conroe to Conroe-1.1 or
Conroe-x.y, but I am missing something that lets us declare "Conroe-1.1
is Conroe-1.2 with this difference", like we do for machines. We surely
don't want to duplicate everything that stays the same for each new CPU
version.

Andreas

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