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7158457: division by zero in adaptiveweightedaverage

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Add ceiling to AdaptiveWeightedAverage

Reviewed-by: ysr, iveresov
This commit is contained in:
Mikael Vidstedt 2012-05-15 00:56:06 +02:00
parent 17b26a6a0c
commit c23595da74
2 changed files with 24 additions and 8 deletions
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14
hotspot/src/share/vm/gc_implementation/shared/gcUtil.cpp
View file

@ -31,9 +31,15 @@ float AdaptiveWeightedAverage::compute_adaptive_average(float new_sample,
float average) {
// We smooth the samples by not using weight() directly until we've
// had enough data to make it meaningful. We'd like the first weight
// used to be 1, the second to be 1/2, etc until we have 100/weight
// samples.
unsigned count_weight = 100/count();
// used to be 1, the second to be 1/2, etc until we have
// OLD_THRESHOLD/weight samples.
unsigned count_weight = 0;
// Avoid division by zero if the counter wraps (7158457)
if (!is_old()) {
count_weight = OLD_THRESHOLD/count();
}
unsigned adaptive_weight = (MAX2(weight(), count_weight));
float new_avg = exp_avg(average, new_sample, adaptive_weight);
@ -43,8 +49,6 @@ float AdaptiveWeightedAverage::compute_adaptive_average(float new_sample,
void AdaptiveWeightedAverage::sample(float new_sample) {
increment_count();
assert(count() != 0,
"Wraparound -- history would be incorrectly discarded");
// Compute the new weighted average
float new_avg = compute_adaptive_average(new_sample, average());

18
hotspot/src/share/vm/gc_implementation/shared/gcUtil.hpp
View file

@ -50,11 +50,20 @@ class AdaptiveWeightedAverage : public CHeapObj {
unsigned _weight; // The weight used to smooth the averages
// A higher weight favors the most
// recent data.
bool _is_old; // Has enough historical data
const static unsigned OLD_THRESHOLD = 100;
protected:
float _last_sample; // The last value sampled.
void increment_count() { _sample_count++; }
void increment_count() {
_sample_count++;
if (!_is_old && _sample_count > OLD_THRESHOLD) {
_is_old = true;
}
}
void set_average(float avg) { _average = avg; }
// Helper function, computes an adaptive weighted average
@ -64,13 +73,15 @@ class AdaptiveWeightedAverage : public CHeapObj {
public:
// Input weight must be between 0 and 100
AdaptiveWeightedAverage(unsigned weight, float avg = 0.0) :
_average(avg), _sample_count(0), _weight(weight), _last_sample(0.0) {
_average(avg), _sample_count(0), _weight(weight), _last_sample(0.0),
_is_old(false) {
}
void clear() {
_average = 0;
_sample_count = 0;
_last_sample = 0;
_is_old = false;
}
// Useful for modifying static structures after startup.
@ -84,7 +95,8 @@ class AdaptiveWeightedAverage : public CHeapObj {
float average() const { return _average; }
unsigned weight() const { return _weight; }
unsigned count() const { return _sample_count; }
float last_sample() const { return _last_sample; }
float last_sample() const { return _last_sample; }
bool is_old() const { return _is_old; }
// Update data with a new sample.
void sample(float new_sample);