linux-kernel - Re: [PATCH v1 1/6] perf report: Sort child tasks by tid

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Date: Wed, 14 Feb 2024 09:42:38 -0800
From: Ian Rogers <irogers@...gle.com>
To: Arnaldo Carvalho de Melo <acme@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Namhyung Kim <namhyung@...nel.org>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Yang Jihong <yangjihong1@...wei.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v1 1/6] perf report: Sort child tasks by tid

On Wed, Feb 14, 2024 at 9:24 AM Arnaldo Carvalho de Melo
<acme@...nel.org> wrote:
>
> On Tue, Feb 13, 2024 at 10:37:03PM -0800, Ian Rogers wrote:
> > Commit 91e467bc568f ("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
> >    1301762  1301762        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
>
>
> Since we're adding extra code for sorting wouldn't be more convenient to
> have this done in an graphically hierarchical output?
>
> But maybe to make this honour asking for a CSV output the above is
> enough? Or can we have both, i.e. for people just doing --tasks, the
> hirarchical way, for CSV, then like above, with the comma separator.
>
> But then perf stat has -x to ask for CSV that is used by the more
> obscure --exclude-other option :-\
>
> Maybe we need a --csv that is consistent accross all tools.

I've no objection to a graphical/CSV output, I was in this code as I
was restructuring it for memory savings. Fixing the output ordering
was a side-effect, the "graphical" sorting/indentation is mentioned as
it is carrying forward a behavior from the previous code but done in a
somewhat different way. Let's have other output things as follow up
work.

Thanks,
Ian

> - Arnaldo