Re: [PATCH 09/10] tracing: Remove obsolete sched_switch tracer

[Steven Rostedt <rostedt@goodmis.org>]

On Tue, 2011-02-08 at 17:16 -0500, Steven Rostedt wrote:
> plain text document attachment
> (0009-tracing-Remove-obsolete-sched_switch-tracer.patch)
> From: Steven Rostedt <srostedt@redhat.com>
> 
> The trace events sched_switch and sched_wakeup do the same thing
> as the stand alone sched_switch tracer does. It is no longer needed.

Hmm, is this the right thing to do, or should we do the "WARN_ONCE()"
when it is used, and give it a year to remove it?

-- Steve

> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  Documentation/trace/ftrace.txt    |  110 -------------------------------------
>  kernel/trace/trace_sched_switch.c |   48 ----------------
>  2 files changed, 0 insertions(+), 158 deletions(-)
> 
> diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
> index 557c1ed..65eddb7 100644
> --- a/Documentation/trace/ftrace.txt
> +++ b/Documentation/trace/ftrace.txt
> @@ -202,10 +202,6 @@ Here is the list of current tracers that may be configured.
>  	to draw a graph of function calls similar to C code
>  	source.
>  
> -  "sched_switch"
> -
> -	Traces the context switches and wakeups between tasks.
> -
>    "irqsoff"
>  
>  	Traces the areas that disable interrupts and saves
> @@ -273,39 +269,6 @@ format, the function name that was traced "path_put" and the
>  parent function that called this function "path_walk". The
>  timestamp is the time at which the function was entered.
>  
> -The sched_switch tracer also includes tracing of task wakeups
> -and context switches.
> -
> -     ksoftirqd/1-7     [01]  1453.070013:      7:115:R   +  2916:115:S
> -     ksoftirqd/1-7     [01]  1453.070013:      7:115:R   +    10:115:S
> -     ksoftirqd/1-7     [01]  1453.070013:      7:115:R ==>    10:115:R
> -        events/1-10    [01]  1453.070013:     10:115:S ==>  2916:115:R
> -     kondemand/1-2916  [01]  1453.070013:   2916:115:S ==>     7:115:R
> -     ksoftirqd/1-7     [01]  1453.070013:      7:115:S ==>     0:140:R
> -
> -Wake ups are represented by a "+" and the context switches are
> -shown as "==>".  The format is:
> -
> - Context switches:
> -
> -       Previous task              Next Task
> -
> -  <pid>:<prio>:<state>  ==>  <pid>:<prio>:<state>
> -
> - Wake ups:
> -
> -       Current task               Task waking up
> -
> -  <pid>:<prio>:<state>    +  <pid>:<prio>:<state>
> -
> -The prio is the internal kernel priority, which is the inverse
> -of the priority that is usually displayed by user-space tools.
> -Zero represents the highest priority (99). Prio 100 starts the
> -"nice" priorities with 100 being equal to nice -20 and 139 being
> -nice 19. The prio "140" is reserved for the idle task which is
> -the lowest priority thread (pid 0).
> -
> -
>  Latency trace format
>  --------------------
>  
> @@ -491,79 +454,6 @@ x494] <- /root/a.out[+0x4a8] <- /lib/libc-2.7.so[+0x1e1a6]
>                     latencies, as described in "Latency
>                     trace format".
>  
> -sched_switch
> -------------
> -
> -This tracer simply records schedule switches. Here is an example
> -of how to use it.
> -
> - # echo sched_switch > current_tracer
> - # echo 1 > tracing_enabled
> - # sleep 1
> - # echo 0 > tracing_enabled
> - # cat trace
> -
> -# tracer: sched_switch
> -#
> -#           TASK-PID   CPU#    TIMESTAMP  FUNCTION
> -#              | |      |          |         |
> -            bash-3997  [01]   240.132281:   3997:120:R   +  4055:120:R
> -            bash-3997  [01]   240.132284:   3997:120:R ==>  4055:120:R
> -           sleep-4055  [01]   240.132371:   4055:120:S ==>  3997:120:R
> -            bash-3997  [01]   240.132454:   3997:120:R   +  4055:120:S
> -            bash-3997  [01]   240.132457:   3997:120:R ==>  4055:120:R
> -           sleep-4055  [01]   240.132460:   4055:120:D ==>  3997:120:R
> -            bash-3997  [01]   240.132463:   3997:120:R   +  4055:120:D
> -            bash-3997  [01]   240.132465:   3997:120:R ==>  4055:120:R
> -          <idle>-0     [00]   240.132589:      0:140:R   +     4:115:S
> -          <idle>-0     [00]   240.132591:      0:140:R ==>     4:115:R
> -     ksoftirqd/0-4     [00]   240.132595:      4:115:S ==>     0:140:R
> -          <idle>-0     [00]   240.132598:      0:140:R   +     4:115:S
> -          <idle>-0     [00]   240.132599:      0:140:R ==>     4:115:R
> -     ksoftirqd/0-4     [00]   240.132603:      4:115:S ==>     0:140:R
> -           sleep-4055  [01]   240.133058:   4055:120:S ==>  3997:120:R
> - [...]
> -
> -
> -As we have discussed previously about this format, the header
> -shows the name of the trace and points to the options. The
> -"FUNCTION" is a misnomer since here it represents the wake ups
> -and context switches.
> -
> -The sched_switch file only lists the wake ups (represented with
> -'+') and context switches ('==>') with the previous task or
> -current task first followed by the next task or task waking up.
> -The format for both of these is PID:KERNEL-PRIO:TASK-STATE.
> -Remember that the KERNEL-PRIO is the inverse of the actual
> -priority with zero (0) being the highest priority and the nice
> -values starting at 100 (nice -20). Below is a quick chart to map
> -the kernel priority to user land priorities.
> -
> -   Kernel Space                     User Space
> - ===============================================================
> -   0(high) to  98(low)     user RT priority 99(high) to 1(low)
> -                           with SCHED_RR or SCHED_FIFO
> - ---------------------------------------------------------------
> -  99                       sched_priority is not used in scheduling
> -                           decisions(it must be specified as 0)
> - ---------------------------------------------------------------
> - 100(high) to 139(low)     user nice -20(high) to 19(low)
> - ---------------------------------------------------------------
> - 140                       idle task priority
> - ---------------------------------------------------------------
> -
> -The task states are:
> -
> - R - running : wants to run, may not actually be running
> - S - sleep   : process is waiting to be woken up (handles signals)
> - D - disk sleep (uninterruptible sleep) : process must be woken up
> -					(ignores signals)
> - T - stopped : process suspended
> - t - traced  : process is being traced (with something like gdb)
> - Z - zombie  : process waiting to be cleaned up
> - X - unknown
> -
> -
>  ftrace_enabled
>  --------------
>  
> diff --git a/kernel/trace/trace_sched_switch.c b/kernel/trace/trace_sched_switch.c
> index 8f758d0..7e62c0a 100644
> --- a/kernel/trace/trace_sched_switch.c
> +++ b/kernel/trace/trace_sched_switch.c
> @@ -247,51 +247,3 @@ void tracing_sched_switch_assign_trace(struct trace_array *tr)
>  	ctx_trace = tr;
>  }
>  
> -static void stop_sched_trace(struct trace_array *tr)
> -{
> -	tracing_stop_sched_switch_record();
> -}
> -
> -static int sched_switch_trace_init(struct trace_array *tr)
> -{
> -	ctx_trace = tr;
> -	tracing_reset_online_cpus(tr);
> -	tracing_start_sched_switch_record();
> -	return 0;
> -}
> -
> -static void sched_switch_trace_reset(struct trace_array *tr)
> -{
> -	if (sched_ref)
> -		stop_sched_trace(tr);
> -}
> -
> -static void sched_switch_trace_start(struct trace_array *tr)
> -{
> -	sched_stopped = 0;
> -}
> -
> -static void sched_switch_trace_stop(struct trace_array *tr)
> -{
> -	sched_stopped = 1;
> -}
> -
> -static struct tracer sched_switch_trace __read_mostly =
> -{
> -	.name		= "sched_switch",
> -	.init		= sched_switch_trace_init,
> -	.reset		= sched_switch_trace_reset,
> -	.start		= sched_switch_trace_start,
> -	.stop		= sched_switch_trace_stop,
> -	.wait_pipe	= poll_wait_pipe,
> -#ifdef CONFIG_FTRACE_SELFTEST
> -	.selftest    = trace_selftest_startup_sched_switch,
> -#endif
> -};
> -
> -__init static int init_sched_switch_trace(void)
> -{
> -	return register_tracer(&sched_switch_trace);
> -}
> -device_initcall(init_sched_switch_trace);
> -