linux-kernel - Re: [PATCH v2 10/15] perf ftrace: add support for trace option sleep-time

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Date:   Tue, 7 Jul 2020 13:09:43 -0300
From:   Arnaldo Carvalho de Melo <acme@...nel.org>
To:     Changbin Du <changbin.du@...il.com>
Cc:     Namhyung Kim <namhyung@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 10/15] perf ftrace: add support for trace option
 sleep-time

Em Tue, Jul 07, 2020 at 11:35:14PM +0800, Changbin Du escreveu:
> On Fri, Jul 03, 2020 at 03:40:59PM +0900, Namhyung Kim wrote:
> > On Sat, Jun 27, 2020 at 10:38 PM Changbin Du <changbin.du@...il.com> wrote:
> > > This adds an option '--graph-nosleep-time' which allow us only to measure
> > > on-CPU time. This option is function_graph tracer only.

> > I'd suggest --graph-sleep-time instead and set it by default.
> > Then we can have --no-graph-sleep-time as well.

> If so can we make --graph-sleep-time as default. Seems there is no something
> like OPT_BOOLEAN_DEFAULT().

> > By the way,  didn't we agree to have something like --graph-opts instead?

> As I mentioned in previous version, --graph-opts make the parsing a little
> complex.
> 	--graph-opts depth=<n>,nosleep_time,noirqs,no_tail,verbose

> While the exsiting style is '--graph-depth <n>'. The cons is we must type more
> characters. The pros is don't need to reimplement parsing and align with old
> behaviour.
> 	--graph-depth <n>
> 	--graph-nosleep-time
> 	--graph-noirqs
> 	--graph-notail
> 	--graph-verbose

This achieves the same result, yes, but it is more cumbersome, to use
all we would have to do:

    perf ftrace --graph-depth 10 --graph-nosleep-time --graph-noirqs --graph-notail --graph-verbose ...

When we could have a more compact:

    perf ftrace --graph-opts depth=10,nosleep-time,noirqs,notail,verbose ...

I.e., instead of a series of:

        OPT_INTEGER(0, "graph-depth", &ftrace.graph_depth, "Max depth for function graph tracer"),
	OPT_BOOLEAN(0, "sleep-time", &ftrace.sleep_time, "explanation"),
	OPT_BOOLEAN(0, "irqs" &ftrace.irqs, "explanation"),
	OPT_BOOLEAN(0, "tail" &ftrace.tail, "explanation"),
	OPT_BOOLEAN(0, "verbose" &ftrace.verbose, "explanation"),

We'd have a:

	OPT_CALLBACK(0, "graph-opts", &ftrace, "options", "graph options", parse_graph_opts),

And parse_graph_opts() would just have a simple strchr(opt, ',') + if
strcmp()/else loop, i.e., it would be easier for users, slightly more
difficult for perf developers :-)

- Arnaldo