RFR: 8352738: Implement JEP 520: JFR Method Timing and Tracing

[Markus Grönlund]

On Thu, 22 May 2025 11:26:21 GMT, Aleksey Shipilev <shade at openjdk.org> wrote:

>> Could I have a review of this enhancement that will add tracing capabilities to JFR? There are opportunities for performance improvements in the implementation, but I would rather add them later and separately.
>> 
>> Testing: tier 1-3, test/jdk/jdk/jfr
>> 
>> Thanks
>> Erik
>
> src/hotspot/share/jfr/recorder/checkpoint/types/traceid/jfrTraceIdMacros.hpp line 54:
> 
>> 52: #define LEAKP_META_BIT                            (BIT << 2)
>> 53: #define LEAKP_BIT                                 (LEAKP_META_BIT << META_SHIFT)
>> 54: #define TIMING_BIT                                LEAKP_BIT // Alias
> 
> I guess there a reason to piggyback on leakp bit? Is this necessary? Sounds like there is still space for this bit? I guess it might be confusing when something like `SET_TIMING_BIT` sets `LEAKP_BIT`?

The number of available bits is precious and must be allocated with care.

Here we have a mutually exclusive situation that allows us to save bits.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25306#discussion_r2104669342