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From: Steven Rostedt on 7 May 2010 09:10


"Frederic Weisbecker" <fweisbec(a)gmail.com> wrote:

>On Mon, May 03, 2010 at 11:40:48PM -0400, Steven Rostedt wrote:
>> From: Steven Rostedt <srostedt(a)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(a)goodmis.org>
>
>
>
>Very nice!!
>
>Acked-by: Frederic Weisbecker <fweisbec(a)gmail.com>
>

Thanks!

-- Steve


--
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