linux-kernel - Re: [PATCHv6 3/4] tracing: graph output support for irqsoff tracer

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Date:	Wed, 14 Apr 2010 09:50:52 +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: [PATCHv6 3/4] tracing: graph output support for irqsoff tracer

On Tue, Apr 13, 2010 at 01:33:37AM +0200, Frederic Weisbecker wrote:
> On Fri, Apr 02, 2010 at 07:01:22PM +0200, Jiri Olsa wrote:
> > +#define GRAPH_TRACER_FLAGS (TRACE_GRAPH_PRINT_CPU | \
> > +			    TRACE_GRAPH_PRINT_PROC)
> > +
> > +static enum print_line_t irqsoff_print_line(struct trace_iterator *iter)
> > +{
> > +	u32 flags = GRAPH_TRACER_FLAGS;
> > +
> > +	if (trace_flags & TRACE_ITER_LATENCY_FMT)
> > +		flags |= TRACE_GRAPH_PRINT_DURATION;
> > +	else
> > +		flags |= TRACE_GRAPH_PRINT_ABS_TIME;
> 
> 
> 
> Why not having ABS_TIME in any case?
> 
> And more important, you probably want to add TRACE_ITER_LATENCY_FMT
> as well to get the contexts (need-resched, hardirq/softirq, preempt-depth,
> lock-depth)

hi,

latency info
	The latency info is governed by global 'trace_flags', the graph tracers
	follows that as well.


absolute time
	The idea was to follow the current irqsoff function trace format. Though
	it cannot be exatly the same, it can print the same info.

	By default I added TRACE_GRAPH_PRINT_CPU and TRACE_GRAPH_PRINT_PROC,
	since they are always there for current irqsoff trace.

	Then the absolute time is printed only in the case when the
	latency info is switched off.

	AFAICS the 'time' field in the output (for latency enabled) actually
	represents the duration	(computed/printed in trace_print_lat_context function).
	Hence I added TRACE_GRAPH_PRINT_DURATION to graph output for the latency case.

	So the answer to your question is, the absolute time is not part
	of the output, since it's not part of the original trace output.
	My opinion is the absolute time is not be that important
	for this tracer, the duration is.


	latency output OFF:

		current tracer:
		TASK-PID    CPU#    TIMESTAMP FUNCTION


		graph tracer:
		TIME        CPU  TASK/PID                      FUNCTION CALLS


	latency output ON:

		current tracer:
				_------=> CPU#
			       / _-----=> irqs-off
			      | / _----=> need-resched
			      || / _---=> hardirq/softirq
			      ||| / _--=> preempt-depth
			      |||| /_--=> lock-depth
			      |||||/       delay
		cmd     pid   |||||| time    |   caller
		   \\   /      ||||||   \\   |   /



		graph tracer:
				      _-----=> irqs-off        
				     / _----=> need-resched    
				    | / _---=> hardirq/softirq 
				    || / _--=> preempt-depth   
				    ||| / _-=> lock-depth      
				    |||| /                     
		CPU  TASK/PID       |||||  DURATION                  FUNCTION CALLS


	Also the non-latency case covers the 'verbose' option output.




thanks for your comments,
hopefully I haven't missed anything.. ;)

jirka
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