RFR: 8365926: RISC-V: Performance regression in renaissance (chi-square) [v5]

[Robbin Ehn]

On Thu, 4 Sep 2025 13:32:34 GMT, Robbin Ehn <rehn at openjdk.org> wrote:

>> Hey, please consider!
>> 
>> A bunch of info in JBS entry, please read that also.
>> 
>> I narrowed this issue down to the old jal optimization, making direct calls when in reach.
>> This patch restores them and removes this regression.
>> 
>> In essence we turn "jalr ra,0(t1)" into a "jal ra,<dest>" if reachable, and restore the jalr if a new destination is not reachable.
>> 
>> Please test on your hardware!
>> 
>> 
>> Chi Square (100 runs each, 10 fastest iterations of each run, P550)
>> JDK-23 (last version with trampoline calls)
>> Mean: 3189.5827
>> Standard Deviation: 284.6478
>> 
>> JDK-25
>> Mean: 3424.8905
>> Standard Deviation: 222.2208
>> 
>> Patch:
>> Mean: 3144.8535
>> Standard Deviation: 229.2577
>> 
>> 
>> No issues found in t1, running t2 also. Stress tested on vf2, bpi-f3, p550.
>
> Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:
> 
>  - Merge branch 'master' into 8365926
>  - Review comments
>  - Review comments
>  - Merge branch 'master' into 8365926
>  - Spelling
>  - Merge branch 'master' into 8365926
>  - draft jal<->jalr

Hamlin had some offline Q so I gather this data for him:

Benchmark Results:

Base: JDK24* +UseTrampoline

JAL OPT: JDK24* +UseTrampoline + JAL OPT


+-----------------+--------------+--------------+----------------+----------------+--------------+------------------+-------------+----------------+------------------+--------------------+
| Benchmark       | Mean (Base)  | SD (Base)    | Fastest (Base) | Mean (JAL OPT) | SD (JAL OPT) | Fastest (JAL OPT)| Diff Mean   | Diff Fastest   | Mean Diff Ratio  | Fastest Diff Ratio |
+-----------------+--------------+--------------+----------------+----------------+--------------+------------------+-------------+----------------+------------------+--------------------+
| future-genetic  | 8317.8449    | 925.0775     | 7824.59        | 8421.137       | 1870.3916    | 7955.19          | 103.2922    | 130.6          | 1.012418145      | 1.01669097         |
| akka-uct        | 54775.8037   | 5220.7361    | 49614.46       | 54149.9939     | 4730.3662    | 48736.7          | -625.8097   | -877.76        | 0.9885750686     | 0.9823083835       |
| movie-lens      | 44859.3268   | 107.8713     | 38160.64       | 43043.6965     | 7932.6525    | 36807.2          | -1815.6295  | -1353.44       | 0.9595261529     | 0.9645330896       |
| scala-doku      | 10792.4933   | 3004.9348    | 970.34         | 10739.0164     | 2692.6155    | 9226.94          | -53.4766    | 256.59         | 0.9950450188     | 1.028605382        |
| chi-square      | 4740.1812    | 3552.9489    | 2579.09        | 4749.0893      | 3484.3178    | 2498.04          | 8.9081      | -81.05         | 1.001879274      | 0.968574187        |
| fj-kmeans       | 18597.656    | 2481.4036    | 17994.43       | 18588.154      | 4458.6089    | 18019.15         | -9.5018     | 24.72          | 0.9994890862     | 1.001373758        |
| db-shootout     | 26529.8048   | 3163.9087    | 21270.43       | 25101.5681     | 2483.0698    | 21419.11         | -1428.2367  | 148.67         | 0.9461648244     | 1.006989986        |
| finagle-http    | 20646.1713   | 1635.9154    | 14898.97       | 20250.4966     | 1046.1738    | 14735.66         | -395.6747   | -163.31        | 0.9808354443     | 0.9890388396       |
| reactors        | 52051.8872   | 2023.7865    | 49188.65       | 51625.9497     | 2150.598     | 48874.49         | -425.9376   | -314.16        | 0.9918170594     | 0.9936131608       |
| dec-tree        | 7532.9295    | 756.8107     | 4076.4         | 7441.0578      | 750.30926    | 4089.08          | -91.8717    | 12.68          | 0.9878039878     | 1.003110588        |
| naive-bayes     | 38973.8684   | 16828.5555   | 31479.37       | 38484.4577     | 16640.458    | 31576.24         | -489.4106   | 96.87          | 0.9874425937     | 1.003077253        |
| als             | 20116.2896   | 42.9005      | 14593.64       | 19553.929      | 947.1711     | 14599.15         | -562.3509   | 5.52           | 0.9720449855     | 1.000377562        |
| par-mnemonics   | 17564.7499   | 744.1041     | 16654.08       | 17239.074      | 1100.0016    | 15942.67         | -325.676    | -711.41        | 0.9814585518     | 0.9572831402       |
| scala-kmeans    | 1201.4918    | 180.6982     | 845            | 1173.5701      | 205.5769     | 791.32           | -27.9217    | -53.68         | 0.9767608069     | 0.9364733728       |
| philosophers    | 4780.9081    | 417.8337     | 3656.22        | 4828.5436      | 1372.1029    | 3926.02          | 47.6356     | 269.8          | 1.009963714      | 1.073792058        |
| log-regression  | 7403.8792    | 8743.3328    | 3675.79        | 7275.2818      | 715.8207     | 3578.2           | -128.5983   | -97.6          | 0.98263097       | 0.9734506052       |
| gauss-mix       | 35128.1145   | 8364.2843    | 27585.27       | 33996.7118     | 7896.5377    | 26810.99         | -1131.4027  | -774.27        | 0.9677921028     | 0.9719313967       |
| mnemonics       | 21426.0608   | 537.9065     | 20202.69       | 20956.9427     | 610.3026     | 19568.55         | -469.1181   | -634.14        | 0.9781052568     | 0.9686111107       |
| dotty           | 16674.7994   | 13824.23     | 12773.145      | 16098.8288     | 13498.268    | 7484.09          | -575.9706   | -247.36        | 0.965458619      | 0.9680060015       |
| finagle-chirper | 20949.0206   | 10776.0049   | 15527.08       | 20286.9623     | 10038.7242   | 15212.05         | -662.0582   | -315.03        | 0.9683966944     | 0.9797109308       |
+-----------------+--------------+--------------+----------------+----------------+--------------+------------------+-------------+----------------+------------------+--------------------+

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

PR Comment: https://git.openjdk.org/jdk/pull/26944#issuecomment-3276121311