Use hardware performance counter data for the detailed/self-profile data view

[wesleywiser]

Now that rustc supports using HPC data in -Zself-profile (rust-lang/rust#78781), it would be great to use this support on perf.rlo as well. Many of our smaller benchmarks don't run long enough for the std::time::Instant based profiling to work reliably which makes it hard to interpret the data when it doesn't really match the results reported on the summary page for a particular benchmark. By using the HPC data, hopefully this will improve the accuracy of detailed data view.

[eddyb]

instructions:u is also the default for the total counts, so it seems natural to compare it, instead of time - often there is a meaningful change in the total instructions:u, but it's lost in time noise in the query view.

Also, assuming it (still) works, I recommend -Z self-profile-counter=instructions-minus-irqs:u (instead of the plain instructions:u), to avoid weird jitter in otherwise-deterministic queries.

[eddyb]

Oh dear, it won't work yet, it's broken without adding features = ["nightly"] or updating the version of measureme that rustc uses (see rust-lang/rust#78781 (comment)).

[wesleywiser]

Opened rust-lang/rust#98471 to update measureme in rustc to resolve that.

[klensy]

Opened rust-lang/rust#98471 to update measureme in rustc to resolve that.

Merged.

[Kobzol]

I have tried to implement this, but I don't know how to actually read the HW counter data from the output of -Zself-profile. I'm using -Zself-profile -Zself-profile-counter=instructions:u, but the output file, when processed with summarize summarize --json, only contains information about time (I don't see any counter values).

[bjorn3]

I think profiles either contain timestamps or instructions:u values, not both. Did you check that summarize summarize --json outputs values that make sense if the counters are time rather than instructions?

[Kobzol]

To be honest, I'm not really sure how to recognize that. It's true that when I turn on HW counters, the times seem to be diferent by orders of magnitude. So the counter values just get stored in the nanos attribute of time?

[lqd]

The PR introducing the feature in rustc did mention this as somewhat backwards compatible for tools, until they adapt to the new counters. Maybe summarize is in that category.

[Kobzol]

Yeah I saw that, but somehow I expected that this adoption has already happened in these 3 years 😅 Maybe not, I'll check how the tools work.

[Kobzol]

Yeah it seems to just output time as nanoseconds.

[Kobzol]

Reopening, because #1647 had to be reverted because of some issue with measureme.