Re: [PATCH v2 1/3] cpu-models: add "disable-deprecated-feats" option to cpu model expansion

[Collin Walling]

On 4/25/24 02:31, Markus Armbruster wrote:
> Collin Walling <walling@linux.ibm.com> writes:
> 
>> On 4/24/24 02:19, Markus Armbruster wrote:
>>> Collin Walling <walling@linux.ibm.com> writes:
>>>
>>>> This optional parameter for query-cpu-model-expansion enables CPU
>>>> model features flagged as deprecated to appear in the resulting
>>>> list of properties.
>>>>
>>>> This commit does not add support beyond adding a new argument
>>>> to the query. All queries with this option present will result
>>>> in an error claiming this option is not supported.
>>>>
>>>> Signed-off-by: Collin Walling <walling@linux.ibm.com>
>>>> ---
>>>>  qapi/machine-target.json         | 7 ++++++-
>>>>  target/arm/arm-qmp-cmds.c        | 7 +++++++
>>>>  target/i386/cpu-sysemu.c         | 7 +++++++
>>>>  target/s390x/cpu_models_sysemu.c | 7 +++++++
>>>>  4 files changed, 27 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/qapi/machine-target.json b/qapi/machine-target.json
>>>> index 29e695aa06..b9da284d2d 100644
>>>> --- a/qapi/machine-target.json
>>>> +++ b/qapi/machine-target.json
>>>> @@ -285,6 +285,10 @@
>>>>  #
>>>>  # @type: expansion type, specifying how to expand the CPU model
>>>>  #
>>>> +# @disable-deprecated-feats: include CPU model features that are
>>>> +#     flagged as deprecated. If supported, these features will appear
>>>> +#     in the properties list paired with false.
>>>
>>> What's the default?
>>>
>>> Which command result(s) does this affect?  Suggest to explain using
>>> unabridged example QMP input and output before and after this series.
>>
>> Fair enough. Bool defaults to false but that's not apparent in the
>> description. I will add more detail.
> 
> I didn't mean to ask for example QMP in the doc comment.  I need you to
> explain the new member to me.  Once I understand what the thing does, I
> may have suggestions on improving the doc comment.
> 
> [...]
> 

Ah, I misunderstood.  The idea behind this "disable-deprecated-feats"
option is to add/override any CPU features that are flagged as
deprecated to the props dictionary (found in the CpuModelInfo struct)
paired with the value false.

For example, the csske feature on s390x is flagged as deprecated.  If a
query-cpu-model-expansion command is created with
"disable-deprecated-feats": true, then the csske feature will show up in
the props list as "csske": false.  This also overrides any user defined
features and props that would show up in the response normally. E.g. if
the same command was executed and "csske": true was provided in the
model's properties by the user, the response will still show "csske":
false since the "disable-deprecated-feats" option takes priority (there
is a discussion with David H regarding which should take precedence --
this is a flaw in this design).

In the below QMP samples I provide a static expansion on a host model.
Pay close attention to the bpb, te, cte, and csske properties.

========
 Before
========

This is how query-cpu-model-expansion may be executed today:

{
  "execute": "query-cpu-model-expansion",
  "arguments": {
    "type": "static",
    "model": {
      "name": "host"
    }
  }
}

{
  "return": {
    "model": {
      "name": "z14.2-base",
      "props": {
        "aen": true,
        "cmmnt": true,
        "aefsi": true,
        "diag318": true,
        "mepoch": true,
        "msa8": true,
        "msa7": true,
        "msa6": true,
        "msa5": true,
        "msa4": true,
        "msa3": true,
        "msa2": true,
        "msa1": true,
        "sthyi": true,
        "edat": true,
        "ri": true,
        "edat2": true,
        "etoken": true,
        "vx": true,
        "ipter": true,
        "mepochptff": true,
        "ap": true,
        "vxeh": true,
        "vxpd": true,
        "esop": true,
        "apqi": true,
        "apft": true,
        "els": true,
        "iep": true,
        "apqci": true,
        "cte": true,            <--
        "ais": true,
        "bpb": true,            <--
        "ctop": true,
        "gs": true,
        "ppa15": true,
        "zpci": true,
        "sea_esop2": true,
        "te": true,             <--
        "cmm": true
      }
    }
  }
}

Note: csske does not even show up here.

=======
 After
=======

This is with the optional "disabled-deprecated-feats":

{
  "execute": "query-cpu-model-expansion",
  "arguments": {
    "type": "static",
    "model": {
      "name": "host"
    },
    "disabled-deprecated-feats": true
  }
}

{
  "return": {
    "model": {
      "name": "z14.2-base",
      "props": {
        "aen": true,
        "cmmnt": true,
        "aefsi": true,
        "diag318": true,
        "mepoch": true,
        "msa8": true,
        "msa7": true,
        "msa6": true,
        "msa5": true,
        "msa4": true,
        "msa3": true,
        "msa2": true,
        "msa1": true,
        "sthyi": true,
        "edat": true,
        "ri": true,
        "edat2": true,
        "etoken": true,
        "vx": true,
        "ipter": true,
        "mepochptff": true,
        "ap": true,
        "vxeh": true,
        "vxpd": true,
        "esop": true,
        "apqi": true,
        "apft": true,
        "els": true,
        "iep": true,
        "apqci": true,
        "cte": false,           <-- overridden
        "ais": true,
        "bpb": false,           <-- overridden
        "ctop": true,
        "gs": true,
        "ppa15": true,
        "zpci": true,
        "sea_esop2": true,
        "te": false,            <-- overridden
        "csske": false          <-- added to the dict
        "cmm": true
      }
    }
  }
}

Now, regarding what I have proposed for v3, this option is gone entirely
and the CpuModelInfo structure has been amended to include a new
(optional) "deprecated-props" array.  As such, a lot of the headache
with requiring compliance or conditionals to satisfy other architectures
is completely gone, as well as the requirement for any additional
options to be provided on the QMP command.

For comparison's sake, here is the v3 QMP:

{
  "execute": "query-cpu-model-expansion",
  "arguments": {
    "type": "static",
    "model": {
      "name": "host"
    }
  }
}

{
  "return": {
    "model": {
      "name": "z14.2-base",
      "deprecated-props": [
        "bpb",
        "te",
        "cte",
        "csske"
      ],
      "props": {
        "aen": true,
        "cmmnt": true,
        "aefsi": true,
        "diag318": true,
        "mepoch": true,
        "msa8": true,
        "msa7": true,
        "msa6": true,
        "msa5": true,
        "msa4": true,
        "msa3": true,
        "msa2": true,
        "msa1": true,
        "sthyi": true,
        "edat": true,
        "ri": true,
        "edat2": true,
        "etoken": true,
        "vx": true,
        "ipter": true,
        "mepochptff": true,
        "ap": true,
        "vxeh": true,
        "vxpd": true,
        "esop": true,
        "apqi": true,
        "apft": true,
        "els": true,
        "iep": true,
        "apqci": true,
        "cte": true,
        "ais": true,
        "bpb": true,
        "ctop": true,
        "gs": true,
        "ppa15": true,
        "zpci": true,
        "sea_esop2": true,
        "te": true,
        "cmm": true
      }
    }
  }
}

Hope this helps to provide more context.  Please let me know if you'd
like more info.  I am leaning towards v3's design more, as it seems a
lot cleaner overall.  I would appreciate your feedback there as well if
you have the time.

Thanks!

[...]

-- 
Regards,
  Collin