Re: [PATCH 09/10][RFC] tracing: Remove duplicate id information inevent structure

[Steven Rostedt]

On Wed, 2010-04-28 at 17:06 -0400, Mathieu Desnoyers wrote:
> * Steven Rostedt (rostedt@xxxxxxxxxxx) wrote:
> > From: Steven Rostedt <srostedt@xxxxxxxxxx>
> > 
> > Now that the trace_event structure is embedded in the ftrace_event_call
> > structure, there is no need for the ftrace_event_call id field.
> > The id field is the same as the trace_event type field.
> > 
> > Removing the id and re-arranging the structure brings down the tracepoint
> > footprint by another 5K.
> 
> I might have missed it, but how exactly is the event type allocated
> uniquely ? Is it barely a duplicate of the call "id" field ?

It is allocated in kernel/trace/trace_events.c.

The code there scans the "_ftrace_events" section to find all the events
that are created, and it assigns the events a unique id. Currently the
id is just copied from the trace_event field to the ftrace_event_call
data. The two are the same.

-- Steve


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