Message-ID: <20090904154058.GB6118@nowhere>
Date:	Fri, 4 Sep 2009 17:41:00 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Albin Tonnerre <albin.tonnerre@...e-electrons.com>
Cc:	srostedt@...hat.com, linux-kernel@...r.kernel.org, mingo@...e.hu
Subject: Re: [PATCH v2] tracing: remove mentioning of legacy latency_trace
	file from documentation

On Mon, Aug 31, 2009 at 10:40:08PM +0200, Albin Tonnerre wrote:
> The latency_trace file got removed a while back by commit
> 886b5b73d71e4027d7dc6c14f5f7ab102201ea6b. This patch fixes the
> documentation to stop mentioning it.
> 
> Signed-off-by: Albin Tonnerre <albin.tonnerre@...e-electrons.com>
> ---
> Changes since v1:
>  - mention that the trace format is configurable through the latency-format
>    option
>  - Fix a couple mistakes related to the timestamps
> 
>  Documentation/trace/ftrace.txt |   64 ++++++++++++++++++++--------------------
>  1 files changed, 32 insertions(+), 32 deletions(-)
> 
> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
> index a39b3c7..5167814 100644
> --- a/Documentation/trace/ftrace.txt
> +++ b/Documentation/trace/ftrace.txt
> @@ -85,26 +85,19 @@ of ftrace. Here is a list of some of the key files:
>  	This file holds the output of the trace in a human
>  	readable format (described below).
>  
> -  latency_trace:
> -
> -	This file shows the same trace but the information
> -	is organized more to display possible latencies
> -	in the system (described below).
> -
>    trace_pipe:
>  
>  	The output is the same as the "trace" file but this
>  	file is meant to be streamed with live tracing.
> -	Reads from this file will block until new data
> -	is retrieved. Unlike the "trace" and "latency_trace"
> -	files, this file is a consumer. This means reading
> -	from this file causes sequential reads to display
> -	more current data. Once data is read from this
> -	file, it is consumed, and will not be read
> -	again with a sequential read. The "trace" and
> -	"latency_trace" files are static, and if the
> -	tracer is not adding more data, they will display
> -	the same information every time they are read.
> +	Reads from this file will block until new data is
> +	retrieved.  Unlike the "trace" file, this file is a
> +	consumer. This means reading from this file causes
> +	sequential reads to display more current data. Once
> +	data is read from this file, it is consumed, and
> +	will not be read again with a sequential read. The
> +	"trace" file is static, and if the tracer is not
> +	adding more data,they will display the same
> +	information every time they are read.
>  
>    trace_options:
>  
> @@ -117,10 +110,10 @@ of ftrace. Here is a list of some of the key files:
>  	Some of the tracers record the max latency.
>  	For example, the time interrupts are disabled.
>  	This time is saved in this file. The max trace
> -	will also be stored, and displayed by either
> -	"trace" or "latency_trace".  A new max trace will
> -	only be recorded if the latency is greater than
> -	the value in this file. (in microseconds)
> +	will also be stored, and displayed by "trace".
> +	A new max trace will only be recorded if the
> +	latency is greater than the value in this
> +	file. (in microseconds)
>  
>    buffer_size_kb:
>  
> @@ -210,7 +203,7 @@ Here is the list of current tracers that may be configured.
>  	the trace with the longest max latency.
>  	See tracing_max_latency. When a new max is recorded,
>  	it replaces the old trace. It is best to view this
> -	trace via the latency_trace file.
> +	trace with the latency-format option enabled.
>  
>    "preemptoff"
>  
> @@ -307,8 +300,8 @@ the lowest priority thread (pid 0).
>  Latency trace format
>  --------------------
>  
> -For traces that display latency times, the latency_trace file
> -gives somewhat more information to see why a latency happened.
> +When the latency-format option is enabled, the trace file gives
> +somewhat more information to see why a latency happened.
>  Here is a typical trace.
>  
>  # tracer: irqsoff
> @@ -380,9 +373,10 @@ explains which is which.
>  
>  The above is mostly meaningful for kernel developers.
>  
> -  time: This differs from the trace file output. The trace file output
> -	includes an absolute timestamp. The timestamp used by the
> -	latency_trace file is relative to the start of the trace.
> +  time: When the latency-format option is enabled, the trace file
> +	output includes a timestamp relative to the start of the
> +	trace. This differs from the output when latency-format
> +	is disabled, which includes an absolute timestamp.
>  
>    delay: This is just to help catch your eye a bit better. And
>  	 needs to be fixed to be only relative to the same CPU.
> @@ -440,7 +434,8 @@ Here are the available options:
>    sym-addr:
>     bash-4000  [01]  1477.606694: simple_strtoul <c0339346>
>  
> -  verbose - This deals with the latency_trace file.
> +  verbose - This deals with the trace file when the
> +            latency-format option is enabled.
>  
>      bash  4000 1 0 00000000 00010a95 [58127d26] 1720.415ms \
>      (+0.000ms): simple_strtoul (strict_strtoul)
> @@ -472,7 +467,7 @@ Here are the available options:
>  		the app is no longer running
>  
>  		The lookup is performed when you read
> -		trace,trace_pipe,latency_trace. Example:
> +		trace,trace_pipe. Example:
>  
>  		a.out-1623  [000] 40874.465068: /root/a.out[+0x480] <-/root/a.out[+0
>  x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
> @@ -481,6 +476,11 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
>  	       every scheduling event. Will add overhead if
>  	       there's a lot of tasks running at once.
>  
> +  latency-format - This option changes the trace. When
> +                   it is enabled, the trace displays
> +                   additional information about the
> +                   latencies, as described in "Latency
> +                   trace format".
>  
>  sched_switch
>  ------------
> @@ -601,7 +601,7 @@ an example:
>   # ls -ltr
>   [...]
>   # echo 0 > tracing_enabled
> - # cat latency_trace
> + # cat trace
>  # tracer: irqsoff
>  #
>  irqsoff latency trace v1.1.5 on 2.6.26
> @@ -708,7 +708,7 @@ is much like the irqsoff tracer.
>   # ls -ltr
>   [...]
>   # echo 0 > tracing_enabled
> - # cat latency_trace
> + # cat trace
>  # tracer: preemptoff
>  #
>  preemptoff latency trace v1.1.5 on 2.6.26-rc8
> @@ -855,7 +855,7 @@ tracers.
>   # ls -ltr
>   [...]
>   # echo 0 > tracing_enabled
> - # cat latency_trace
> + # cat trace
>  # tracer: preemptirqsoff
>  #
>  preemptirqsoff latency trace v1.1.5 on 2.6.26-rc8
> @@ -1016,7 +1016,7 @@ Instead of performing an 'ls', we will run 'sleep 1' under
>   # echo 1 > tracing_enabled
>   # chrt -f 5 sleep 1
>   # echo 0 > tracing_enabled
> - # cat latency_trace
> + # cat trace
>  # tracer: wakeup
>  #
>  wakeup latency trace v1.1.5 on 2.6.26-rc8


Hmm, you may want to add the following line:

	echo latency-format > trace_option

to the 4 above to keep the examples relevants.

That's fine, I'll add them and queue up this patch, thanks!

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