8374307: Fix deoptimization storm caused by Action_none in GraphKit::uncommon_trap

[bulasevich]

We observed a deoptimization storm caused by GraphKit::uncommon_trap generator logic. GraphKit::uncommon_trap considers the too_many_recompiles metric. If the threshold is overflowed, it replaces Deoptimization::Action_reinterpret with Deoptimization::Action_none (see code snippet below).

This replacement changes the uncommon_trap logic: once execution hits a trap, the VM performs deoptimization but does not recompile the method anymore. In an "unlucky" case, when the code part calling this uncommon_trap becomes frequent, a deoptimization storm occurs (thousands of deoptimizations per second) causing a significant performance drop.

The original problematic method, which triggered repeated recompilations, is a high-performance compressed binary serialization algorithm with heavy use of conditional branches driven by bitmasks. See a standalone synthetic benchmark to reproduce the issue.

The issue arises when the method overcomes a global recompilation threshold before stabilizing specific trap counters.

Current thresholds:

• Recompilation Limit (too_many_recompiles):
  Condition: decompile_count() >= (PerMethodRecompilationCutoff / 2) + 1
  Default: 201 (derived from default PerMethodRecompilationCutoff = 400).
• Specific Trap Limits (too_many_traps):
  Checks if the trap count for a specific reason exceeds:
  PerMethodTrapLimit (Default: 100) - for Reason_unstable_if, Reason_unstable_fused_if, etc.
  PerMethodSpecTrapLimit (Default: 5000) - for Reason_speculate_class_check, Reason_speculate_null_check, etc.

With the gived defaults, if the only reason for the method recompilation is unstable_if, the system stabilizes after 100 traps (PerMethodTrapLimit). However, if the method experiences traps and recompilations for different reasons, the total number of recompilations can exceed 200 before hitting the limit for unstable_if traps. This triggers Action_none and causes the deopt storm.

The proposal is a minimal change in GraphKit::uncommon_trap: apply the same too_many_recompiles threshold inside Parse::path_is_suitable_for_uncommon_trap - this ensures that on the final recompilation C2 gets a hint not to speculate on untaken branches anymore.

As an alternative solution, we can revisit GraphKit::uncommon_trap. This "Temporary fix" has persisted in the codebase for 17 years, so it is probably time to change it as well. Any comments are welcome

  case Deoptimization::Action_reinterpret:
    // Temporary fix for 6529811 to allow virtual calls to be sure they
    // get the chance to go from mono->bi->mega
    if (!keep_exact_action &&
        Deoptimization::trap_request_index(trap_request) < 0 &&
        too_many_recompiles(reason)) {
      // This BCI is causing too many recompilations.
      if (C->log() != nullptr) {
        C->log()->elem("observe that='trap_action_change' reason='%s' from='%s' to='none'",
                Deoptimization::trap_reason_name(reason),
                Deoptimization::trap_action_name(action));
      }
      action = Deoptimization::Action_none;
      trap_request = Deoptimization::make_trap_request(reason, action);
    } else {
      C->set_trap_can_recompile(true);
    }

---

Progress

• Change must be properly reviewed (1 review required, with at least 1 Reviewer)
• Change must not contain extraneous whitespace
• Commit message must refer to an issue

Issue

• JDK-8374307: Fix deoptimization storm caused by Action_none in GraphKit::uncommon_trap (Bug - P3)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/28966/head:pull/28966
$ git checkout pull/28966

Update a local copy of the PR:
$ git checkout pull/28966
$ git pull https://git.openjdk.org/jdk.git pull/28966/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 28966

View PR using the GUI difftool:
$ git pr show -t 28966

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/28966.diff

Using Webrev

Link to Webrev Comment

[bridgekeeper]

👋 Welcome back bulasevich! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@bulasevich The following label will be automatically applied to this pull request:

• hotspot-compiler

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing list. If you would like to change these labels, use the /label pull request command.

[mlbridge]

Webrevs

• 00: Full (258a9673)

[merykitty]

You can use Compile::too_many_traps_or_recompile here.