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

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Date:	Wed, 21 Oct 2009 09:38:35 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.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 07:33:40PM +0200, Frederic Weisbecker wrote:
> 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...

I like this one, I think it could be done for both iterator and
consuming mode hence ending up with one way of handling this.

I'll repost soon hopefully... :)

thanks,
jirka
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