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

Masami Hiramatsu
2018-02-05T15:14:28Z

(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@linux-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@kernel.org>