linux-kernel - Re: [PATCH 2/4] tracing: add trace

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Date:   Tue, 21 Jul 2020 12:43:42 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Tingwei Zhang <tingwei@...eaurora.org>
Cc:     Ingo Molnar <mingo@...hat.com>, tsoni@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Mao Jinlong <jinlmao@...eaurora.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] tracing: add trace_export support for event trace

On Tue, 21 Jul 2020 12:37:33 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Mon, 20 Jul 2020 10:21:15 +0800
> Tingwei Zhang <tingwei@...eaurora.org> wrote:
> 
> > Only function traces can be exported to other destinations currently.
> > This patch exports event trace as well.
> > 
> > Signed-off-by: Tingwei Zhang <tingwei@...eaurora.org>
> > ---
> >  kernel/trace/trace.c | 24 +++++++++++++-----------
> >  1 file changed, 13 insertions(+), 11 deletions(-)
> > 
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index bb62269724d5..aef6330836e2 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -2697,17 +2697,6 @@ int tracepoint_printk_sysctl(struct ctl_table *table, int write,
> >  	return ret;
> >  }
> >  
> > -void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
> > -{
> > -	if (static_key_false(&tracepoint_printk_key.key))
> > -		output_printk(fbuffer);
> > -
> > -	event_trigger_unlock_commit_regs(fbuffer->trace_file, fbuffer->buffer,
> > -				    fbuffer->event, fbuffer->entry,
> > -				    fbuffer->flags, fbuffer->pc, fbuffer->regs);
> > -}
> > -EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
> > -  
> 
> Please move the ftrace_exports routines up, instead of moving the
> trace_event_buffer_commit() down. As it fits better where it is (next
> to the other buffer_commit code).
> 
> -- Steve
> 
> 
> >  /*
> >   * Skip 3:
> >   *
> > @@ -2868,6 +2857,19 @@ int unregister_ftrace_export(struct
> > trace_export *export) }
> >  EXPORT_SYMBOL_GPL(unregister_ftrace_export);
> >  
> > +void trace_event_buffer_commit(struct trace_event_buffer *fbuffer)
> > +{
> > +	if (static_key_false(&tracepoint_printk_key.key))
> > +		output_printk(fbuffer);
> > +
> > +	if (static_branch_unlikely(&ftrace_exports_enabled))
> > +		ftrace_exports(fbuffer->event);

I would also recommend making each static branch a separate variable.
That way you could pick and choose what you want to enable. If you only
want events, and functions are being traced, it will add a bit of
overhead to handle the functions to just ignore them.

That is:

 ftrace_exports_enabled, trace_event_exports_enabled,
 trace_marker_exports_enabled.

-- Steve


> > +	event_trigger_unlock_commit_regs(fbuffer->trace_file,
> > fbuffer->buffer,
> > +				    fbuffer->event, fbuffer->entry,
> > +				    fbuffer->flags, fbuffer->pc,
> > fbuffer->regs); +}
> > +EXPORT_SYMBOL_GPL(trace_event_buffer_commit);
> > +
> >  void
> >  trace_function(struct trace_array *tr,
> >  	       unsigned long ip, unsigned long parent_ip, unsigned
> > long flags,  
>