AW: [patch] trace: Add user-space event tracing/injection

[Reichert, Hans-Peter]

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-----Ursprüngliche Nachricht-----
Von: Ingo Molnar [mailto:mingo@xxxxxxx]
Gesendet: Donnerstag, 18. November 2010 19:57
An: Reichert, Hans-Peter
Cc: linux-kernel@xxxxxxxxxxxxxxx; Peter Zijlstra; Thomas Gleixner; Arnaldo Carvalho de Melo; Frédéric Weisbecker
Betreff: Re: [patch] trace: Add user-space event tracing/injection


* hp <hp.reichert@xxxxxx> wrote:

> Ingo Molnar <mingo <at> elte.hu> writes:
>
> >
> >
> > * Darren Hart <dvhart <at> linux.intel.com> wrote:
> >
> > > Ideally I would like to see something just like trace_printf()
> > > without having to define it myself in each of my testcases. [...]
> >
> > We can make the prctl a single-argument thing, at the cost of not allowing \0
> in the
> > content. (which is probably sane anyway)
> >
> > That way deployment is super-simple:
> >
> >     prctl(35, "My Trace Message");
> >     ...
> >
> >     if (asprintf(&msg, "My Trace Message: %d\n", 1234) != -1) {
> >             prctl(35, *msg);
> >             free(*msg);
> >     }
> >
> > Thanks,
> >
> >     Ingo
> >
> I like this approach - it is doing it nearly the same way I did it with an extra
> k-mod (no patch needed) and a debugfs entry handled in that mod.
> I only see one thing with the string only data - I am doing stuff where there
> are long recording times with also a lot of user events,
> in such an environment I need more semantics on the event contents.
> In my k-mod solution there's an event ID and the opportunity to log binary data.
> As prctl() has 4 additional args after the option, it would be possible to use
> it in the following way:
> prtctl( 35, int eventID, int data_type, int msglen, void *buf);
> or without the data_type
> prtctl( 35, int eventID, int msglen, void *buf);
> decoding would be of more effort but it would be worth
>
> The event definition would be like this (with data_type):
>
> TRACE_EVENT(user,
>         TP_PROTO(int id, int dtype, int dlen, unsigned char *bytes),
>         TP_ARGS(id, dtype, dlen, bytes),
>         TP_STRUCT__entry(
>                 __field(int, ev_id)
>                 __field(int, ev_type)
>                 __dynamic_array(unsigned char, ev_data, dlen)
>         ),
>         TP_fast_assign(
>                 __entry->ev_id = id;
>               __entry->ev_type = dtype;
>               memcpy(__get_dynamic_array(ev_data), bytes, dlen);
>         ),
>
>         TP_printk("ID: %d type: %s data: %s", __entry->ev_id,
> __print_symbolic(__entry->ev_type, {0,"V"}, {1,"I"}, {2,"S"}, {4,"B"}),
> __entry->ev_type == 0 ? "n/a" : __get_str(ev_data))
> );
>
>
> What do you think about this?

The transport was not limited to strings - it's a memory buffer of 'len' bytes.

In that sense 'ev_id' and 'ev_type' above is really just hardcoding something that
the app might not care about.

For example with the patch i sent one could send 1 byte messages - no other
overhead. (beyond the standard record header)

While if an app does want to use an (ev_id, ev_type), it can still do so. Or if an
app wants to do some other message type, that can be done too - it's free-form.

Thanks,

        Ingo

I agree.
The reason for this was to have a format description that could be used within "trace-cmd report"
without having the need to implement a separate decoder for (each) user land application.
I did a lot of system tracing for the last 10years on a different 'NX system.
>From an analysts sight it is more than just convenience that the tracing format is the same for every application,
just think of a system that is build up of binaries of several suppliers - like it will be in automotive projects.
Having a uniform format description would highly increase usage and acceptance.

Thanks
/hp




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