* [ltt-dev] [RFC] New UST 2.0 Tracepoint Event API
[not found] ` <BLU0-SMTP952D5E28B173886307A86596200@phx.gbl>
@ 2011-08-31 14:38 ` Mathieu Desnoyers
2011-09-01 9:50 ` Nathan Scott
0 siblings, 1 reply; 3+ messages in thread
From: Mathieu Desnoyers @ 2011-08-31 14:38 UTC (permalink / raw)
* Mathieu Desnoyers (compudj at krystal.dyndns.org) wrote:
> * Nathan Scott (nathans at debian.org) wrote:
> [...]
> > > I was also wondering if putting a "loglevel" information (could be
> > > optional) into the TRACEPOINT_EVENT declaration would be useful ? This
> > > could define log levels such as debug, info, warning, and error.
> > >
> >
> > I think that'd be useful - ETW does this on Windows, FWIW.
> > Being able to enable/disable these sub-classes of events is probably useful
> > and it shows the programmers general intent with each event too.
>
> Hrm, I thought about this loglevel idea a little more, and it does not
> seem like it belongs directly into TRACEPOINT_EVENT(). Although tracing
> *can* do logging, tracing is not logging. Therefore, it makes no sense
> to require information that is logging-specific to be declared for all
> tracepoints.
>
> I foresee that we could eventually add API members to support loglevels
> defined alongside with the tracepoint instrumentation, e.g.:
>
> TRACEPOINT_LOGLEVEL_ENUM(
> TP_LOGLEVEL(TP_LOG_DEBUG, 0),
> TP_LOGLEVEL(TP_LOG_WARN, 1),
> ...
> )
>
> TRACEPOINT_EVENT(
> some_tp_name,
> rest of standard tracepoint declaration, without any loglevel
> whatsoever...
> )
>
> TRACEPOINT_LOGLEVEL(some_tp_name, TP_LOG_DEBUG)
>
> With this, libust could export the application loglevels, along with the
> event name to loglevel mappings. I don't plan to implement this API
> right now though.
>
> Thoughts ?
I have a client who would like this API to appear in UST 2.0 headers
soon so they can use it in their instrumentation (even before those
macros are actually implemented). So I think it makes sense to settle on
this:
#ifndef TRACEPOINT_LOGLEVEL
/*
* Tracepoint Loglevel Declaration Facility
*
* This is a place-holder the tracepoint loglevel declaration,
* overridden by the tracer implementation.
*
* Typical use of these loglevels:
*
* 1) Declare the mapping between loglevel names and an integer values
* within TRACEPOINT_LOGLEVEL_ENUM, using TP_LOGLEVEL for each tuple.
* Do _NOT_ add comma (,) nor semicolon (;) between the
* TRACEPOINT_LOGLEVEL_ENUM entries. Do _NOT_ add comma (,) nor
* semicolon (;) after the TRACEPOINT_LOGLEVEL_ENUM declaration. The
* name should be a proper C99 identifier.
*
* TRACEPOINT_LOGLEVEL_ENUM(
* TP_LOGLEVEL( < loglevel_name >, < value > )
* TP_LOGLEVEL( < loglevel_name >, < value > )
* ...
* )
*
* e.g.:
*
* TRACEPOINT_LOGLEVEL_ENUM(
* TP_LOGLEVEL(LOG_EMERG, 0)
* TP_LOGLEVEL(LOG_ALERT, 1)
* TP_LOGLEVEL(LOG_CRIT, 2)
* TP_LOGLEVEL(LOG_ERR, 3)
* TP_LOGLEVEL(LOG_WARNING, 4)
* TP_LOGLEVEL(LOG_NOTICE, 5)
* TP_LOGLEVEL(LOG_INFO, 6)
* TP_LOGLEVEL(LOG_DEBUG, 7)
* )
*
* 2) Then, declare tracepoint loglevels for tracepoints. The first
* field is the name of the tracepoint, the second field is the
* loglevel name.
*
* TRACEPOINT_LOGLEVEL(< [com_company_]project_[component_]event >,
* < loglevel_name >)
*
* The TRACEPOINT_SYSTEM must be defined when declaring a
* TRACEPOINT_LOGLEVEL_ENUM and TRACEPOINT_LOGLEVEL. The tracepoint
* loglevel enumeration apply to the entire TRACEPOINT_SYSTEM. Only one
* tracepoint loglevel enumeration should be declared per tracepoint
* system.
*/
#define TRACEPOINT_LOGLEVEL_ENUM()
#define TRACEPOINT_LOGLEVEL(name, loglevel)
#endif /* #ifndef TRACEPOINT_LOGLEVEL */
So although I cannot say with a 100% confidence level that this will not
change when I will implement the actual macros (planned for this Fall),
I am fairly confident we should be fine with this API.
Feedback is, as always, welcome.
Thanks,
Mathieu
--
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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