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datas tuning fix#98743
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ghost commentedFeb 21, 2024
Tagging subscribers to this area: @dotnet/gc Issue Detailswill add description soon.
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| } | ||
| float mean (float* arr, int size) | ||
| { |
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Worth checking if size > 0 as a precondition check?
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I've added an assert in slope which makes more sense.
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kind of similar to log_with_base, is the assertion/condition intended formean or callers ofmean? If it's a precondition formean, then I would expect the precondition check to be inmean (or bothmean and the callers).
Or ifmean is supposed to support some callers with a negative size, then the final return probably needs to be something likereturn (size > 0) ? (sum / size) : 0
| size_t gc_heap::get_num_completed_gcs () | ||
| float log_with_base (float x, float base) | ||
| { |
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Is it worth asserting if x and base > 0?
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it's actually meant to have x > base and should be enforced. but I can still add an assert.
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log_b(x) is fine forx <= base (e.g., log_2(2) = 1, log_4(2) = 1/2)
I think you're saying (by "should be enforced") that current call site(s) expectx > base.log_with_base is a very reasonable helper function that could get used elsewhere without such a restriction. Or maybe you want to rename it to show that it is intended as a helper for a specific context rather than a general log helper?
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Maoni0 commentedFeb 22, 2024
v2-base is the baseline and v2-rc3 is this change, 4 runs each.    |
| uint64_telapsed_between_gcs;// time between gcs in microseconds (this should really be between_pauses) | ||
| uint64_tgc_pause_time;// pause time for this GC | ||
| uint64_tmsl_wait_time; | ||
| size_tgc_survived_size; |
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| size_tgc_survived_size; | |
| size_tgc_survived_size;// total survived size across all relevant generations for this GC |
i.e., it's -not- gen0 to be consistent in what is being recorded
| // | ||
| // We need to observe the history of tcp's so record them in a small buffer. | ||
| // | ||
| floatrecorded_tcp_rearranged[recorded_tcp_array_size]; |
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You've mentioned this before, but this is doable without copying the data (though I think the real concern would be avoiding the additional concept of "rearranged" data rather than the copy of a small amount data, which easily could be negligible in cost.
Encapsulating the data in a circular buffer with an iterator would probably accomplish this - probably makes sense to this as a follow-up PR which I can do.
| floatrecorded_tcp_rearranged[recorded_tcp_array_size]; | ||
| floatrecorded_tcp[recorded_tcp_array_size]; | ||
| intrecorded_tcp_index; | ||
| inttotal_recorded_tcp; |
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| inttotal_recorded_tcp; | |
| inttotal_recorded_tcp;// can exceed the array size |
| recorded_tcp_index++; | ||
| if (recorded_tcp_index==recorded_tcp_array_size) | ||
| { | ||
| recorded_tcp_index=0; | ||
| } |
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| recorded_tcp_index++; | |
| if (recorded_tcp_index==recorded_tcp_array_size) | |
| { | |
| recorded_tcp_index=0; | |
| } | |
| recorded_tcp_index= (recorded_tcp_index+1) %recorded_tcp_array_size; |
| if (total_recorded_tcp >=recorded_tcp_array_size) | ||
| { | ||
| intearlier_entry_size=recorded_tcp_array_size-recorded_tcp_index; | ||
| memcpy (recorded_tcp_rearranged, (recorded_tcp+recorded_tcp_index), (earlier_entry_size*sizeof (float))); |
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Can we use std::copy in this project to avoid the manual byte size computation?
| returncopied_count; | ||
| } | ||
| inthighest_avg_recorded_tcp (intcount,floatavg,float*highest_avg) |
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This name is a bit confusing to me. It looks like it returns the average and count of the elements above a limit (which happens to be the average, given the name of the parameter, but it isn't relevant to this function that it's the average).
| floathighest_sum=0.0; | ||
| inthighest_count=0; | ||
| for (inti=0;i<count;i++) |
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I think this is using thecount oldest elements in the buffer - should it be newest?
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note -count is the entire buffer (as returned by the rearrange method and passed back in here), so there isn't a correctness issue here
| floatrecorded_tcp_rearranged[recorded_tcp_array_size]; | ||
| floatrecorded_tcp[recorded_tcp_array_size]; | ||
| intrecorded_tcp_index; | ||
| inttotal_recorded_tcp; |
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recorded_tcp_count to be consistent with other naming?
| // each time our calculation tells us to shrink. | ||
| intdec_failure_count; | ||
| intdec_failure_recheck_threshold; | ||
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For later - I think it would be interesting to share the increment/decrement cases to avoid some duplication. It would have to be parameterized in some way so that the behavior could be customized. Anyways, there's no requested change here right now.
| floatbelow_target_accumulation; | ||
| floatbelow_target_threshold; | ||
| // Currently only used for dprintf. |
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#ifdef this?
| // Recording the gen2 GC indices so we know how far apart they are. Currently unused | ||
| // but we should consider how much value there is if they are very far apart. | ||
| size_tgc_index; | ||
| // This is (gc_elapsed_time / time inbetween this and the last gen2 GC) |
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nit - "in between" or even just "between"
| // at the beginning of a BGC and the PM triggered full GCs | ||
| // fall into this case. | ||
| PER_HEAP_ISOLATED_FIELD_DIAG_ONLYuint64_tsuspended_start_time; | ||
| // Right now this is diag only but may be used functionally later. |
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I don't think this comment really adds anything
| dynamic_heap_count_data.sample_index = (dynamic_heap_count_data.sample_index + 1) % dynamic_heap_count_data_t::sample_size; | ||
| (dynamic_heap_count_data.current_samples_count)++; |
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It bugs me a bit that the sample and recorded tcp handling are different (one inline here, the other in helper methods), but I think that's for another day.
| } | ||
| } | ||
| float avg_x = (float)sum_x / n; |
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| float avg_x = (float)sum_x / n; | |
| float avg_x = ((float)sum_x) / n; |
or thestatic_cast<float>(sum_x) / n format requires parenthesis
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also below, though I don't think those explicit casts are needed since avg_x is a float. fine to be careful though of course.
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also this is just (n+1) / 2.0f, though the loop is still needed for dprintf
| // Change it to a desired number if you want to print. | ||
| int max_times_to_print_tcp = 0; | ||
| // Return the slope, and the average values in the avg arg. |
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Is there a name for the slope that is being calculated here? I see that it's a weighted sum based on distance from the middle, but I'm not familiar with that. For example, I don't think this is the slope of a typical regression line? (which is fine, though I guess I'm a bit curious about the mathematical properties of this)
| } | ||
| float median_throughput_cost_percent = median_of_3 (throughput_cost_percents[0], throughput_cost_percents[1], throughput_cost_percents[2]); | ||
| float avg_throughput_cost_percent = (float)((throughput_cost_percents[0] + throughput_cost_percents[1] + throughput_cost_percents[2]) / 3.0); |
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nit - might be able to drop the(float) if you used3.0f
| if (dynamic_heap_count_data.dec_failure_count) | ||
| { | ||
| (dynamic_heap_count_data.dec_failure_count)++; | ||
| } | ||
| else | ||
| { | ||
| dynamic_heap_count_data.dec_failure_count = 1; | ||
| } |
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I don't think thisif is necessary.
| if (shrink_p && step_down_int && (new_n_heaps > step_down_int)) | ||
| { | ||
| // TODO - if we see that it wants to shrink by 1 heap too many times, we do want to shrink. |
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also if n_heaps is small, then 1 is significant
(well, significant to the heap count, if the gc heap is a small fraction of overall memory, which it might be if the heap count is small, then the memory savings could still be insignificant)
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My review is very late for the preview release. These aren't necessary right now and can be addressed in a future PR.
sebastienros commentedApr 5, 2024 • edited
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Just for visibility as people started asking about this, I believe this introduced a slight RPS regression in the native aot benchmarks. Windows and Linux.
And we can see an improvement in max working set
NB: The unstable results are unrelated and were tracked in#98021 |
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trending up/down (and if so how fast is that trend) and make a decision if we want to grow/shrink according to our calculation
There are a few issues with these that will be addressed in future checkins -