linux-kernel - Re: [PATCH] tracing - fix function graph trace to properly skip records

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Date:	Tue, 20 Oct 2009 19:33:40 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
Cc:	mingo@...e.hu, rostedt@...dmis.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tracing - fix function graph trace to properly skip
	records

On Tue, Oct 20, 2009 at 07:11:54PM +0200, Frederic Weisbecker wrote:
> > NOTE:
> > 
> > AFAIK patch does not affect "trace_pipe" handling, since the change is
> > on the ring_buffer_iter level. However the "trace_pipe" suffers from
> > the same issue -> when the read buffer is filled up, the current trace
> > entry is not copied to it. Following read will continue with next entry.
> > It might be harder to fix this, since "trace_pipe" in order to see next
> > record has to eat the current one... 
> > 
> > I'll look at possible solution, but any ideas are welcome.. :)
> > 

Yeah, dealing with the ring buffer consuming mode is more tricky.
Actually I would feel more comfortable with a generic solution that
solves consuming and iter modes.

We have a private field in struct trace_iterator so I guess
we can store useful things inside.

Say we have that in the ring buffer:

f1 entry
f1 return
f2 entry

If we know we are a leaf call, we need to store a copy of the
f1 entry/f1 return couple in struct trace_iterator::private
So that we can check that on the next processing and call
print_graph_entry_leaf() directly.

What remains is the need to check the status of the last
processing. Was it TRACE_TYPE_HANLED,TRACE_TYPE_PARTIAL_LINE..?

We probably need this info in trace_iterator...

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