linux-kernel - Re: [PATCH] tracing/ftrace: better manage the context info for events

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Date:	Fri, 30 Jan 2009 10:34:46 -0200
From:	Arnaldo Carvalho de Melo <acme@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tracing/ftrace: better manage the context info for
	events

Em Fri, Jan 30, 2009 at 12:59:05AM -0800, Frederic Weisbecker escreveu:
> Impact: make trace_event more convenient for tracers
> 
> All tracers (for the moment) that use the struct trace_event want to have
> the context info printed before their own output: the pid/cmdline, cpu, and timestamp.
> 
> But some other tracers that want to implement their trace_event callbacks will
> not necessary need these information or they may want to format them as they want.
> 
> This patch adds a new default-enabled trace option: TRACE_ITER_CONTEXT_INFO
> When disabled through:
> 
> echo nocontext-info > /debugfs/tracing/trace_options
> 
> The pid, cpu and timestamps headers will not be printed.
> 
> IE with the sched_switch tracer with context-info (default):
> 
>             bash-2935  [001]   100.356561:   2935:120:S ==> [001]     0:140:R <idle>
>           <idle>-0     [000]   100.412804:      0:140:R   + [000]    11:115:S events/0
>           <idle>-0     [000]   100.412816:      0:140:R ==> [000]    11:115:R events/0
>         events/0-11    [000]   100.412829:     11:115:S ==> [000]     0:140:R <idle>
> 
> Without context-info:
> 
>   2935:120:S ==> [001]     0:140:R <idle>
>      0:140:R   + [000]    11:115:S events/0
>      0:140:R ==> [000]    11:115:R events/0
>     11:115:S ==> [000]     0:140:R <idle>
> 
> A tracer can disable it at runtime by clearing the bit TRACE_ITER_CONTEXT_INFO in trace_flags.
> 
> Moreover, two callbacks have been added inside trace_event:
> _ context_info() which let a tracer override the format of the context info
> _ lat_context_info() which do the same with the latency_trace file
> 
> If they are not defined, the usual way of printing the context info will be used.

Please wait a bit, I'm trying to use it and the first thing I notice was
that I need the trace_iterator in the context callback, to get the
timestamp.

- Arnaldo
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