linux-kernel - Re: [PATCH 00/18] [ANNOUNCE] Dynamically created function based events

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Date:   Tue, 6 Feb 2018 00:14:28 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        rostedt <rostedt@...dmis.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        linux-rt-users <linux-rt-users@...r.kernel.org>,
        linux-trace-users <linux-trace-users@...r.kernel.org>,
        acme <acme@...nel.org>, Clark Williams <williams@...hat.com>,
        Jiri Olsa <jolsa@...hat.com>, bristot <bristot@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Jonathan Corbet <corbet@....net>,
        Namhyung Kim <namhyung@...nel.org>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>
Subject: Re: [PATCH 00/18] [ANNOUNCE] Dynamically created function based
 events

(Note that I also agree with Linus's opinion that this is
 like a debugger, since I already did it in perf-probe :))

On Sun, 4 Feb 2018 11:39:39 -0800
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> (Obviously it's not entirely black-and-white, but I do think there is
> a pretty big difference between the two groups. And the first group
> will obviously use the explicit trace points _too_, generally to
> narrow down where they want to go with the function-based one).
> 
> We'll see. Maybe I'm entirely wrong. But I'm hoping that the
> function-based one will end up being helpful.

BTW, if the function-based tracing is helpful for both of them,
they can start using it back in 2010 because kprobe-based tracer
already supported it.

It was less announced, I must admit that I was lazy at that point.
Also, since I moved usability effort on perf-probe, kprobe-based
event syntax is not so funcy.

"SyS_openat(int dfd, string path, x32 flags, x16 mode)"

is equal to

"p SyS_openat dfd=%di:x64 path=%si:string flags=%dx:x32 mode=%cx:x16"

in kprobe probe definition syntax, but with perf-probe and CONFIG_DEBUG_INFO,

perf probe -a 'sys_openat $params'

will setup the event correctly.

So, we need to clarify what will attract more "2nd group" people to
function based events. E.g. the events for EXPORT_SYMBOL_GPL() symbols
already defined and easily on/off.

Thank you,

-- 
Masami Hiramatsu <mhiramat@...nel.org>