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8350758: G1: Use actual last prediction in accumulated survivor rate prediction too #23795

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8350758: G1: Use actual last prediction in accumulated survivor rate prediction too #23795

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8350758
tschatzl Feb 26, 2025
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* ayang review
tschatzl Feb 27, 2025
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21 changes: 9 additions & 12 deletions src/hotspot/share/gc/g1/g1SurvRateGroup.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -68,26 +68,23 @@ void G1SurvRateGroup::stop_adding_regions() {
_accum_surv_rate_pred = REALLOC_C_HEAP_ARRAY(double, _accum_surv_rate_pred, _num_added_regions, mtGC);
_surv_rate_predictors = REALLOC_C_HEAP_ARRAY(TruncatedSeq*, _surv_rate_predictors, _num_added_regions, mtGC);

// Assume that the prediction for the newly added regions is the same as the
// ones at the (current) end of the array. Particularly predictions at the end
// of this array fairly seldom get updated, so having a better initial value
// that is at least somewhat related to the actual application is preferable.
double new_pred = _stats_arrays_length > 1
? _accum_surv_rate_pred[_stats_arrays_length - 1] - _accum_surv_rate_pred[_stats_arrays_length - 2]
: InitialSurvivorRate;

for (uint i = _stats_arrays_length; i < _num_added_regions; ++i) {
// Initialize predictors and accumulated survivor rate predictions.
_surv_rate_predictors[i] = new TruncatedSeq(10);
if (i == 0) {
_surv_rate_predictors[i]->add(InitialSurvivorRate);
_accum_surv_rate_pred[i] = 0.0;
_accum_surv_rate_pred[i] = InitialSurvivorRate;
} else {
_surv_rate_predictors[i]->add(_surv_rate_predictors[i-1]->last());
_accum_surv_rate_pred[i] = _accum_surv_rate_pred[i-1] + new_pred;
// Assume that the prediction for the newly added regions is the same as the
// ones at the (current) end of the array. Particularly predictions at the end
// of this array fairly seldom get updated, so having a better initial value
// that is at least somewhat related to the actual application is preferable.
double next_pred = _surv_rate_predictors[i-1]->last();
_surv_rate_predictors[i]->add(next_pred);
_accum_surv_rate_pred[i] = _accum_surv_rate_pred[i-1] + next_pred;
}
}
_last_pred = new_pred;
_last_pred = _surv_rate_predictors[_num_added_regions-1]->last();

_stats_arrays_length = _num_added_regions;
}
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