linux-kernel - Re: [RFC PATCH v3 4/4] trace: Trace log handler for logging into STM blocks

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Date:	Wed, 8 Jul 2015 09:19:28 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Chunyan Zhang <zhang.chunyan@...aro.org>, mingo@...hat.com,
	mathieu.poirier@...aro.org, serge.broslavsky@...aro.org,
	broonie@...nel.org, alexander.shishkin@...ux.intel.com,
	zhang.lyra@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH v3 4/4] trace: Trace log handler for logging into
 STM blocks

On Wed, 8 Jul 2015 14:31:48 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Tue, Jul 07, 2015 at 06:10:43PM +0800, Chunyan Zhang wrote:
> > Add the function 'trace_event_stm_output_##call' for printing events
> > trace log into STM blocks.
> > 
> > This patch also adds a function call at where the events have been
> > committed to ring buffer to export the trace event information to
> > STM blocks.
> 
> So then you have two copies of the data, why that? Would a scheme were
> data either goes to the STM or the regular buffer not make much more
> sense?
> 
> > +++ b/include/trace/perf.h
> > @@ -175,6 +175,7 @@ trace_event_raw_event_##call(void *__data, proto)			\
> >  	{ assign; }							\
> >  									\
> >  	trace_event_buffer_commit(&fbuffer);				\
> > +	trace_event_stm_log(&fbuffer);					\
> 
> This makes every trace event slower.

Of course this could use a jump label.

But I agree, I think a switch to which buffer it should be sent to is
better. I could come up with a way to make the buffer more generic, and
have it switch between where the event is recorded.

-- Steve

> 
> >  }
> >  /*
> >   * The ftrace_test_probe is compiled out, it is only here as a build time check

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