RFR: 8366847: JFR reports incorrect number of cores on hybrid CPU [v5]

[Yasumasa Suenaga]

On Wed, 8 Oct 2025 06:14:03 GMT, Yasumasa Suenaga <ysuenaga at openjdk.org> wrote:

>> src/hotspot/share/jfr/metadata/metadata.xml line 855:
>> 
>>> 853: 
>>> 854:   <Event name="CPUInformation" category="Operating System, Processor" label="CPU Information"
>>> 855:          description="Characteristics and descriptions of the processor(s) the JVM is running on. Note that "cores" field would be incorrect on hybrid CPU."
>> 
>> Perhaps better stated on the cores field:
>> 
>> <Field type="uint" name="cores" label="Cores (approximation on a hybrid CPU" />
>> 
>> ? But really this is for JFR folk to decide. Do these labels get used for GUI tools like JMC?
>> 
>> BTW I assume that "hwThreads" is the number of logical processors - right?
>
>> BTW I assume that "hwThreads" is the number of logical processors - right?
> 
> Yes

> Perhaps better stated on the cores field:

Thanks for your comment! I added that sentence to `description` attribute in `Field` element.
After this change, flight record contains following metadata. I believe it would be parsed in some tools like JMC (JMC shows the description as a tooltip)


$ jfr metadata --events jdk.CPUInformation /tmp/test.jfr
@Name("jdk.CPUInformation")
@Category({"Operating System", "Processor"})
@Label("CPU Information")
@Description("Characteristics and descriptions of the processor(s) the JVM is running on")
class CPUInformation extends jdk.jfr.Event {
  @Label("Start Time")
  @Timestamp("TICKS")
  long startTime;

  @Label("Type")
  String cpu;

  @Label("Description")
  String description;

  @Unsigned
  @Label("Sockets")
  int sockets;

  @Unsigned
  @Label("Cores")
  @Description("Approximation on a hybrid CPU")
  int cores;

  @Unsigned
  @Label("Hardware Threads")
  int hwThreads;
}

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PR Review Comment: https://git.openjdk.org/jdk/pull/27080#discussion_r2412763021