linux-kernel - Re: [RFC/PATCHSET 0/5] perf ftrace: Implement function latency histogram (v1)

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Date:   Tue, 30 Nov 2021 16:36:49 -0800
From:   Stephane Eranian <eranian@...gle.com>
To:     Namhyung Kim <namhyung@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        Jiri Olsa <jolsa@...hat.com>, Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Ian Rogers <irogers@...gle.com>,
        Song Liu <songliubraving@...com>,
        Changbin Du <changbin.du@...il.com>
Subject: Re: [RFC/PATCHSET 0/5] perf ftrace: Implement function latency
 histogram (v1)

On Tue, Nov 30, 2021 at 2:58 PM Namhyung Kim <namhyung@...nel.org> wrote:
>
> Hi Arnaldo,
>
> On Tue, Nov 30, 2021 at 6:37 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > Em Mon, Nov 29, 2021 at 03:18:25PM -0800, Namhyung Kim escreveu:
> > > Hello,
> > >
> > > I've implemented 'latency' subcommand in the perf ftrace command to
> > > show a histogram of function latency.
> > >
> > > To handle new subcommands, the existing functionality is moved to
> > > 'trace' subcommand while preserving backward compatibility of not
> > > having a subcommand at all (defaults to 'trace').
> > >
> > > The latency subcommand accepts a target (kernel, for now) function
> > > with -T option and shows a histogram like below:
> >
> > Humm, wouldn't be interesting to shorten this by having a new 'perf
> > flat' (function latency) tool, on the same level as 'perf ftrace' and
> > leave 'perf ftrace' to just being a convenient perf interface to what
> > ftrace provides?
>
> That would be fine.  I also think 'perf ftrace latency' is
> bit too long.  But if we would add a new feature
> like argdist (in BCC) later, I thought it'd be nice being
> a subcommand in the perf ftrace together.
>
> But it's up to you.  I'll make a change if you prefer
> 'flat' (or how about 'fnlat' instead?).
>
I am not too fond of the flat option because as we had more bpf tools
like function latency, then we keep extending the list of commands
each with a small span which is different
from what we have right now.