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Merged
PeterSolMS merged 3 commits into from
Jul 16, 2021
Merged

Add a time-based decay to the linear allocation model. #55174

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cdc50ac
Add a time-based decay to the linear allocation model.
PeterSolMS Jul 5, 2021
24a65c7
Remove extraneous empty lines.
PeterSolMS Jul 7, 2021
13f87e0
Corrected a problem in the computation of the new allocation pointed …
PeterSolMS Jul 14, 2021
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Add a time-based decay to the linear allocation model. 
Real world scenario that motivated this allocated a huge amount of data once a day, leading to high gen 0 and gen 1 budgets (several GB).

After this, there was relatively little activity, cause gen 1 budget to take several hours to normalize.

The new logic discounts the previous desired allocation over a period of 5 minutes.
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@PeterSolMS
PeterSolMS committed Jul 5, 2021
commit cdc50ac84ee126408a7c797ebc21dcdbfb7eeae9
27 changes: 14 additions & 13 deletions src/coreclr/gc/gc.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -20254,6 +20254,7 @@ void gc_heap::update_collection_counts ()
}

dd_gc_clock (dd) = dd_gc_clock (dd0);
dd_previous_time_clock (dd) = dd_time_clock (dd);
dd_time_clock (dd) = now;
}
}
Expand Down Expand Up @@ -36701,6 +36702,7 @@ bool gc_heap::init_dynamic_data()
dynamic_data* dd = dynamic_data_of (i);
dd->gc_clock = 0;
dd->time_clock = now;
dd->previous_time_clock = now;
dd->current_size = 0;
dd->promoted_size = 0;
dd->collection_count = 0;
Expand All @@ -36726,21 +36728,17 @@ float gc_heap::surv_to_growth (float cst, float limit, float max_limit)
//not be correct (collection happened too soon). Correct with a linear estimation based on the previous
//value of the budget
static size_t linear_allocation_model (float allocation_fraction, size_t new_allocation,
size_t previous_desired_allocation, size_t collection_count)
size_t previous_desired_allocation, float time_since_previous_collection_secs)
{
if ((allocation_fraction < 0.95) && (allocation_fraction > 0.0))
{
const float decay_time = 5*60.0f; // previous desired allocation expires over 5 minutes
float decay_factor = (decay_time <= time_since_previous_collection_secs) ?
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@mangod9 mangod9 Jul 6, 2021

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will we build a test scenario in GCPerfSim to validate that the decay has the desired effect?

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@PeterSolMS PeterSolMS Jul 7, 2021

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I will try, but it may be a bit involved.

0 :
((decay_time - time_since_previous_collection_secs) / decay_time);
dprintf (2, ("allocation fraction: %d", (int)(allocation_fraction/100.0)));
new_allocation = (size_t)(allocation_fraction*new_allocation + (1.0-allocation_fraction)*previous_desired_allocation);
new_allocation = (size_t)(allocation_fraction*new_allocation + (1.0-allocation_fraction)*decay_factor*previous_desired_allocation);
}
#if 0
size_t smoothing = 3; // exponential smoothing factor
if (smoothing > collection_count)
smoothing = collection_count;
new_allocation = new_allocation / smoothing + ((previous_desired_allocation / smoothing) * (smoothing-1));
#else
UNREFERENCED_PARAMETER(collection_count);
#endif //0
return new_allocation;
}

Expand All @@ -36767,6 +36765,9 @@ size_t gc_heap::desired_new_allocation (dynamic_data* dd,
float f = 0;
size_t max_size = dd_max_size (dd);
size_t new_allocation = 0;
float time_since_previous_collection_secs = (dd_time_clock (dd) - dd_previous_time_clock (dd))*1e-6f;


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@mangod9 mangod9 Jul 6, 2021

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Nit: remove one empty line?

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@PeterSolMS PeterSolMS Jul 7, 2021

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Looking at the code, I think I should remove both of the empty lines - no reason to separate the declarations here, I think.

float allocation_fraction = (float) (dd_desired_allocation (dd) - dd_gc_new_allocation (dd)) / (float) (dd_desired_allocation (dd));

if (gen_number >= max_generation)
Expand All @@ -36793,7 +36794,7 @@ size_t gc_heap::desired_new_allocation (dynamic_data* dd,
new_allocation = max((new_size - current_size), min_gc_size);

new_allocation = linear_allocation_model (allocation_fraction, new_allocation,
dd_desired_allocation (dd), dd_collection_count (dd));
dd_desired_allocation (dd), time_since_previous_collection_secs);

if (
#ifdef BGC_SERVO_TUNING
Expand Down Expand Up @@ -36845,7 +36846,7 @@ size_t gc_heap::desired_new_allocation (dynamic_data* dd,
max ((current_size/4), min_gc_size));

new_allocation = linear_allocation_model (allocation_fraction, new_allocation,
dd_desired_allocation (dd), dd_collection_count (dd));
dd_desired_allocation (dd), time_since_previous_collection_secs);

}
}
Expand All @@ -36857,7 +36858,7 @@ size_t gc_heap::desired_new_allocation (dynamic_data* dd,
new_allocation = (size_t) min (max ((f * (survivors)), min_gc_size), max_size);

new_allocation = linear_allocation_model (allocation_fraction, new_allocation,
dd_desired_allocation (dd), dd_collection_count (dd));
dd_desired_allocation (dd), time_since_previous_collection_secs);

if (gen_number == 0)
{
Expand Down
7 changes: 7 additions & 0 deletions src/coreclr/gc/gcpriv.h
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Expand Up @@ -885,6 +885,7 @@ class dynamic_data
size_t fragmentation; //fragmentation when we don't compact
size_t gc_clock; //gc# when last GC happened
uint64_t time_clock; //time when last gc started
uint64_t previous_time_clock; // time when previous gc started
size_t gc_elapsed_time; // Time it took for the gc to complete
float gc_speed; // speed in bytes/msec for the gc to complete

Expand Down Expand Up @@ -5004,6 +5005,12 @@ uint64_t& dd_time_clock (dynamic_data* inst)
{
return inst->time_clock;
}
inline
uint64_t& dd_previous_time_clock (dynamic_data* inst)
{
return inst->previous_time_clock;
}


inline
size_t& dd_gc_clock_interval (dynamic_data* inst)
Expand Down