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Indicate change in RSS from start to end of pass in time-passes output #81771

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Feb 5, 2021
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Indicate change in RSS from start to end of pass in time-passes output #81771

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25 changes: 11 additions & 14 deletions compiler/rustc_data_structures/src/profiling.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -590,24 +590,21 @@ pub fn print_time_passes_entry(
end_rss: Option<usize>,
) {
let rss_to_mb = |rss| (rss as f64 / 1_000_000.0).round() as usize;
let rss_change_to_mb = |rss| (rss as f64 / 1_000_000.0).round() as i128;

let mem_string = match (start_rss, end_rss) {
(Some(start_rss), Some(end_rss)) => {
// It's tempting to add the change in RSS from start to end, but its somewhat confusing
// and misleading when looking at time-passes output. Consider two adjacent entries:
//
// time: 10.000; rss start: 1000MB, end: 1000MB, change: 0MB pass1
// time: 5.000; rss start: 2000MB, end: 2000MB, change: 0MB pass2
//
// If you're looking for jumps in RSS based on the change column, you miss the fact
// that a 1GB jump happened between pass1 and pass2 (supposing pass1 and pass2 actually
// occur sequentially and pass1 isn't just nested within pass2). It's easy to imagine
// someone missing this or being confused by the fact that the change is zero.

format!("; rss: {:>5}MB -> {:>5}MB", rss_to_mb(start_rss), rss_to_mb(end_rss))
let change_rss = end_rss as i128 - start_rss as i128;

format!(
"; rss: {:>4}MB -> {:>4}MB ({:>+5}MB)",
rss_to_mb(start_rss),
rss_to_mb(end_rss),
rss_change_to_mb(change_rss),
)
}
(Some(start_rss), None) => format!("; rss start: {:>5}MB", rss_to_mb(start_rss)),
(None, Some(end_rss)) => format!("; rss end: {:5>}MB", rss_to_mb(end_rss)),
(Some(start_rss), None) => format!("; rss start: {:>4}MB", rss_to_mb(start_rss)),
(None, Some(end_rss)) => format!("; rss end: {:>4}MB", rss_to_mb(end_rss)),
(None, None) => String::new(),
};

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