Commit b11c53e1 authored May 25, 2009 by Zhaolei Committed by Frederic Weisbecker May 26, 2009

ftrace: Add task_comm support for trace_event



If we enable a trace event alone without any tracer running (such as
function tracer, sched switch tracer, etc...) it can't output enough
task command information.

We need to use the tracing_{start/stop}_cmdline_record() helpers
which are designed to keep track of cmdlines for any tasks that
were scheduled during the tracing.

Before this patch:
 # echo 1 > debugfs/tracing/events/sched/sched_switch/enable
 # cat debugfs/tracing/trace
 # tracer: nop
 #
 #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
 #              | |       |          |         |
            <...>-2289  [000] 526276.724790: sched_switch: task bash:2289 [120] ==> sshd:2287 [120]
            <...>-2287  [000] 526276.725231: sched_switch: task sshd:2287 [120] ==> bash:2289 [120]
            <...>-2289  [000] 526276.725452: sched_switch: task bash:2289 [120] ==> sshd:2287 [120]
            <...>-2287  [000] 526276.727181: sched_switch: task sshd:2287 [120] ==> swapper:0 [140]
           <idle>-0     [000] 526277.032734: sched_switch: task swapper:0 [140] ==> events/0:5 [115]
            <...>-5     [000] 526277.032782: sched_switch: task events/0:5 [115] ==> swapper:0 [140]
 ...

After this patch:
 # tracer: nop
 #
 #           TASK-PID    CPU#    TIMESTAMP  FUNCTION
 #              | |       |          |         |
             bash-2269  [000] 527347.989229: sched_switch: task bash:2269 [120] ==> sshd:2267 [120]
             sshd-2267  [000] 527347.990960: sched_switch: task sshd:2267 [120] ==> bash:2269 [120]
             bash-2269  [000] 527347.991143: sched_switch: task bash:2269 [120] ==> sshd:2267 [120]
             sshd-2267  [000] 527347.992959: sched_switch: task sshd:2267 [120] ==> swapper:0 [140]
           <idle>-0     [000] 527348.531989: sched_switch: task swapper:0 [140] ==> events/0:5 [115]
         events/0-5     [000] 527348.532115: sched_switch: task events/0:5 [115] ==> swapper:0 [140]
 ...

Changelog:
v1->v2: Update Kconfig to select CONTEXT_SWITCH_TRACER in
        ENABLE_EVENT_TRACING
v2->v3: v2 can solve problem that was caused by config EVENT_TRACING
        alone, but when CONFIG_FTRACE is off and CONFIG_TRACING is
        selected by other config, compile fail happened again.
        This version solves it.

[ Impact: fix incomplete output of event tracing ]

Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Cc: Tom Zanussi <tzanussi@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
LKML-Reference: <4A14FDFE.2080402@cn.fujitsu.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>

parent 29fcefba

kernel/trace/Kconfig

+7 −2

Original line number	Diff line number	Diff line
		@@ -49,6 +49,11 @@ config FTRACE_NMI_ENTER
		default y

		config EVENT_TRACING
		select CONTEXT_SWITCH_TRACER
		bool

		config CONTEXT_SWITCH_TRACER
		select MARKERS
		bool

		config TRACING
		@@ -176,10 +181,10 @@ config SCHED_TRACER
		This tracer tracks the latency of the highest priority task
		to be scheduled in, starting from the point it has woken up.

		config CONTEXT_SWITCH_TRACER
		config ENABLE_CONTEXT_SWITCH_TRACER
		bool "Trace process context switches"
		select TRACING
		select MARKERS
		select CONTEXT_SWITCH_TRACER
		help
		This tracer gets called from the context switch and records
		all switching of tasks.

kernel/trace/trace_events.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -85,6 +85,7 @@ static void ftrace_clear_events(void)

		if (call->enabled) {
		call->enabled = 0;
		tracing_stop_cmdline_record();
		call->unregfunc();
		}
		}
		@@ -99,12 +100,14 @@ static void ftrace_event_enable_disable(struct ftrace_event_call *call,
		case 0:
		if (call->enabled) {
		call->enabled = 0;
		tracing_stop_cmdline_record();
		call->unregfunc();
		}
		break;
		case 1:
		if (!call->enabled) {
		call->enabled = 1;
		tracing_start_cmdline_record();
		call->regfunc();
		}
		break;
		@@ -1058,6 +1061,7 @@ static void trace_module_remove_events(struct module *mod)
		found = true;
		if (call->enabled) {
		call->enabled = 0;
		tracing_stop_cmdline_record();
		call->unregfunc();
		}
		if (call->event)
		@@ -1262,11 +1266,13 @@ static __init void event_trace_self_tests(void)
		}

		call->enabled = 1;
		tracing_start_cmdline_record();
		call->regfunc();

		event_test_stuff();

		call->unregfunc();
		tracing_stop_cmdline_record();
		call->enabled = 0;

		pr_cont("OK\n");