Matcher    : {do_mir_borrowck}
Matches    : 577
Not Matches: 746
Percentage : 43%

Tree
| matched `{do_mir_borrowck}` (43% total, 0% self)
: | rustc_borrowck::nll::compute_regions (20% total, 0% self)
: : | rustc_borrowck::nll::type_check::type_check_internal (13% total, 0% self)
: : : | core::ops::function::FnOnce::call_once (5% total, 0% self)
: : : : | rustc_borrowck::nll::type_check::liveness::generate (5% total, 3% self)
: : : | <rustc_borrowck::nll::type_check::TypeVerifier<'a, 'b, 'tcx> as rustc::mir::visit::Visitor<'tcx>>::visit_mir (3% total, 0% self)
: | rustc::mir::visit::Visitor::visit_mir (8% total, 6% self)
: | <rustc_borrowck::MirBorrowckCtxt<'cx, 'tcx> as rustc_mir_dataflow::DataflowResultsConsumer<'cx, 'tcx>>::visit_statement_entry (5% total, 0% self)
: | rustc_mir_dataflow::do_dataflow (3% total, 0% self)
```

What happens with `--tree-callees` is that

- we find each sample matching the regular expression
- we look at the code that occurs *after* the regex match and try
  to build up a call tree

The `--tree-min-percent 3` option says "only show me things that take
more than 3% of the time". Without this, the tree often gets really
noisy and includes random stuff like the innards of
malloc. `--tree-max-depth` can be useful too, it just limits how many
levels we print.

For each line, we display the percent of time in that function
altogether ("total") and the percent of time spent in **just that
function and not some callee of that function** (self). Usually
"total" is the more interesting number, but not always.

### Relative percentages

By default, all in perf-focus are relative to the **total program
execution**. This is useful to help you keep perspective — often as
we drill down to find hot spots, we can lose sight of the fact that,
in terms of overall program execution, this "hot spot" is actually not
important. It also ensures that percentages between different queries
are easily compared against one another.

That said, sometimes it's useful to get relative percentages, so `perf
focus` offers a `--relative` option. In this case, the percentages are
listed only for samples that match (vs all samples). So for example we
could get our percentages relative to the borrowck itself
like so:

```bash
$ perf focus '{do_mir_borrowck}' --tree-callees --relative --tree-max-depth 1 --tree-min-percent 5
Matcher    : {do_mir_borrowck}
Matches    : 577
Not Matches: 746
Percentage : 100%

Tree
| matched `{do_mir_borrowck}` (100% total, 0% self)
: | rustc_borrowck::nll::compute_regions (47% total, 0% self) [...]
: | rustc::mir::visit::Visitor::visit_mir (19% total, 15% self) [...]
: | <rustc_borrowck::MirBorrowckCtxt<'cx, 'tcx> as rustc_mir_dataflow::DataflowResultsConsumer<'cx, 'tcx>>::visit_statement_entry (13% total, 0% self) [...]
: | rustc_mir_dataflow::do_dataflow (8% total, 1% self) [...]
```

Here you see that `compute_regions` came up as "47% total" — that
means that 47% of `do_mir_borrowck` is spent in that function. Before,
we saw 20% — that's because `do_mir_borrowck` itself is only 43% of
the total time (and `.47 * .43 = .20`).