Commit 91e467bc56 ("perf machine: Use hashtable for machine
threads") made the iteration of thread tids unordered. The perf report
--tasks output now shows child threads in an order determined by the
hashing. For example, in this snippet tid 3 appears after tid 256 even
though they have the same ppid 2:
```
$ perf report --tasks
% pid tid ppid comm
0 0 -1 |swapper
2 2 0 | kthreadd
256 256 2 | kworker/12:1H-k
693761 693761 2 | kworker/10:1-mm
13017621301762 2 | kworker/1:1-mm_
1302530 1302530 2 | kworker/u32:0-k
3 3 2 | rcu_gp
...
```
The output is easier to read if threads appear numerically
increasing. To allow for this, read all threads into a list then sort
with a comparator that orders by the child task's of the first common
parent. The list creation and deletion are created as utilities on
machine. The indentation is possible by counting the number of
parents a child has.
With this change the output for the same data file is now like:
```
$ perf report --tasks
% pid tid ppid comm
0 0 -1 |swapper
1 1 0 | systemd
823 823 1 | systemd-journal
853 853 1 | systemd-udevd
3230 3230 1 | systemd-timesyn
3236 3236 1 | auditd
3239 3239 3236 | audisp-syslog
3321 3321 1 | accounts-daemon
...
```
Signed-off-by: Ian Rogers <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Yang Jihong <yangjihong1@huawei.com>
Cc: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Link: https://lore.kernel.org/r/20240301053646.1449657-2-irogers@google.com
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