RFR: 8356027: Print enhanced compilation timings [v6]

Aleksey Shipilev shade at openjdk.org
Tue May 6 09:31:31 UTC 2025


> In Leyden, we have the extended compilation timings printouts with -XX:+PrintCompilation / UL, that are very useful to study compiler dynamics. These timings include:
>  1. Time spent before queuing: shows the compilation queue bottlenecks
>  2. Time spent in the queue: shows delays caused by queue bottlenecks and compiler load
>  3. Time spent actually compiling: shows the per-method compilation costs
> 
> We should consider the same kind of printout for mainline. This would also require us to print the compilation task _after_ the compilation, not only before it. This improvement would also obviate any need for `PrintCompilation2` flag, [JDK-8356028](https://bugs.openjdk.org/browse/JDK-8356028).
> 
> The difference from the output format we ship in Leyden:
>  1. This output prints before/after the compilation to maintain old behavior partially. The "before" printout is now prepended with `started` to clearly mark it as such.
>  2. The output is raw number in microseconds. In Leyden repo, we have these prepended with characters, like `C0.1`, but that prepending makes it a bit inconvenient with scripts. This PR also does microseconds, instead of fractional milliseconds. This should be enough to capture the wide range of durations.
> 
> See the sample `-XX:+PrintCompilation` output in the comments.
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `compiler`
>  - [x]  Linux x86_64 server fastdebug, `all`

Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:

  Also handle UL printing

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/24984/files
  - new: https://git.openjdk.org/jdk/pull/24984/files/18da4d7c..90462389

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=24984&range=05
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=24984&range=04-05

  Stats: 26 lines in 3 files changed: 15 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/24984.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/24984/head:pull/24984

PR: https://git.openjdk.org/jdk/pull/24984


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