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SubjectRe: [PATCH 3/9 - v2][RFC] tracing: Remove per event trace registering
On Mon, May 03, 2010 at 11:40:48PM -0400, Steven Rostedt wrote:
> From: Steven Rostedt <srostedt@redhat.com>
>
> This patch removes the register functions of TRACE_EVENT() to enable
> and disable tracepoints. The registering of a event is now down
> directly in the trace_events.c file. The tracepoint_probe_register()
> is now called directly.
>
> The prototypes are no longer type checked, but this should not be
> an issue since the tracepoints are created automatically by the
> macros. If a prototype is incorrect in the TRACE_EVENT() macro, then
> other macros will catch it.



Agreed. Typechecking matters for human code but not in this context.
Considering that the tracepoint and the probe are created by the same
CPP code, bugs will be tracked down quickly and located to a single
place.




>
> The trace_event_class structure now holds the probes to be called
> by the callbacks. This removes needing to have each event have
> a separate pointer for the probe.
>
> To handle kprobes and syscalls, since they register probes in a
> different manner, a "reg" field is added to the ftrace_event_class
> structure. If the "reg" field is assigned, then it will be called for
> enabling and disabling of the probe for either ftrace or perf. To let
> the reg function know what is happening, a new enum (trace_reg) is
> created that has the type of control that is needed.
>
> With this new rework, the 82 kernel events and 616 syscall events
> has their footprint dramatically lowered:
>
> text data bss dec hex filename
> 5788186 1337252 9351592 16477030 fb6b66 vmlinux.orig
> 5792282 1333796 9351592 16477670 fb6de6 vmlinux.class
> 5793448 1333780 9351592 16478820 fb7264 vmlinux.tracepoint
> 5796926 1337748 9351592 16486266 fb8f7a vmlinux.data
> 5774316 1306580 9351592 16432488 fabd68 vmlinux.regs
>
> The size went from 16477030 to 16432488, that's a total of 44K
> in savings. With tracepoints being continuously added, this is
> critical that the footprint becomes minimal.
>
> v2: Changed the callback probes to pass void * and typecast the
> value within the function.
>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>



Very nice!!

Acked-by: Frederic Weisbecker <fweisbec@gmail.com>



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