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Fix json output in the self-profiler #56091

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Nov 23, 2018
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Fix json output in the self-profiler #56091

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15 changes: 13 additions & 2 deletions src/librustc/util/profiling.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -93,16 +93,27 @@ macro_rules! define_categories {
$(
let (hits, total) = self.query_counts.$name;

//normalize hits to 0%
let hit_percent =
if total > 0 {
((hits as f32) / (total as f32)) * 100.0
} else {
0.0
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You could use Laplace smoothing instead - (1 + hits) / (2 + total).
It's really simple, but still useful when you want to count almost any kind of interesting/all fractions.

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If not, then r=me

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I'm intrigued but I don't think I completely understand the idea. In the case where the category has no data hits=0 and total=0 so wouldn't this result in (1 + 0) / (2 + 0) => 1/2 => 0.5 aka 50% cache hits when there were no hits or attempts at all?

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Yeah, if there's zero prior knowledge then the cache hit probability is 50% - it's either hit or not :)

If you have some better prior knowledge than that, then you can tweak the α parameter in (α + hits)/(2α + total).
Either way you won't have to divide by zero.

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It just seems like a bug to me that if there's no data, cache hit ratio would be 50%. If it's ok with you, I'd prefer to leave the code as is. :)

};

json.push_str(&format!(
"{{ \"category\": {}, \"time_ms\": {},
\"query_count\": {}, \"query_hits\": {} }}",
\"query_count\": {}, \"query_hits\": {} }},",
stringify!($name),
self.times.$name / 1_000_000,
total,
format!("{:.2}", (((hits as f32) / (total as f32)) * 100.0))
format!("{:.2}", hit_percent)
));
)*

//remove the trailing ',' character
json.pop();

json.push(']');

json
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