2 files changed, 84 insertions, 26 deletions

diff --git a/Documentation/trace/events-power.txt b/Documentation/trace/events-power.txt
index cf794af22855..e1498ff8cf94 100644
--- a/Documentation/trace/events-power.txt
+++ b/Documentation/trace/events-power.txt
@@ -17,7 +17,7 @@ Cf. include/trace/events/power.h for the events definitions.
 1. Power state switch events
 ============================
 
-1.1 New trace API
+1.1 Trace API
 -----------------
 
 A 'cpu' event class gathers the CPU-related events: cpuidle and
@@ -41,31 +41,6 @@ The event which has 'state=4294967295' in the trace is very important to the use
 space tools which are using it to detect the end of the current state, and so to
 correctly draw the states diagrams and to calculate accurate statistics etc.
 
-1.2 DEPRECATED trace API
-------------------------
-
-A new Kconfig option CONFIG_EVENT_POWER_TRACING_DEPRECATED with the default value of
-'y' has been created. This allows the legacy trace power API to be used conjointly
-with the new trace API.
-The Kconfig option, the old trace API (in include/trace/events/power.h) and the
-old trace points will disappear in a future release (namely 2.6.41).
-
-power_start             "type=%lu state=%lu cpu_id=%lu"
-power_frequency         "type=%lu state=%lu cpu_id=%lu"
-power_end               "cpu_id=%lu"
-
-The 'type' parameter takes one of those macros:
- . POWER_NONE   = 0,
- . POWER_CSTATE = 1,    /* C-State */
- . POWER_PSTATE = 2,    /* Frequency change or DVFS */
-
-The 'state' parameter is set depending on the type:
- . Target C-state for type=POWER_CSTATE,
- . Target frequency for type=POWER_PSTATE,
-
-power_end is used to indicate the exit of a state, corresponding to the latest
-power_start event.
-
 2. Clocks events
 ================
 The clock events are used for clock enable/disable and for
diff --git a/Documentation/trace/ftrace.txt b/Documentation/trace/ftrace.txt
index 6f51fed45f2d..53d6a3c51d87 100644
--- a/Documentation/trace/ftrace.txt
+++ b/Documentation/trace/ftrace.txt
@@ -1842,6 +1842,89 @@ an error.
  # cat buffer_size_kb
 85
 
+Snapshot
+--------
+CONFIG_TRACER_SNAPSHOT makes a generic snapshot feature
+available to all non latency tracers. (Latency tracers which
+record max latency, such as "irqsoff" or "wakeup", can't use
+this feature, since those are already using the snapshot
+mechanism internally.)
+
+Snapshot preserves a current trace buffer at a particular point
+in time without stopping tracing. Ftrace swaps the current
+buffer with a spare buffer, and tracing continues in the new
+current (=previous spare) buffer.
+
+The following debugfs files in "tracing" are related to this
+feature:
+
+  snapshot:
+
+        This is used to take a snapshot and to read the output
+        of the snapshot. Echo 1 into this file to allocate a
+        spare buffer and to take a snapshot (swap), then read
+        the snapshot from this file in the same format as
+        "trace" (described above in the section "The File
+        System"). Both reads snapshot and tracing are executable
+        in parallel. When the spare buffer is allocated, echoing
+        0 frees it, and echoing else (positive) values clear the
+        snapshot contents.
+        More details are shown in the table below.
+
+        status\input  |     0      |     1      |    else    |
+        --------------+------------+------------+------------+
+        not allocated |(do nothing)| alloc+swap |   EINVAL   |
+        --------------+------------+------------+------------+
+        allocated     |    free    |    swap    |   clear    |
+        --------------+------------+------------+------------+
+
+Here is an example of using the snapshot feature.
+
+ # echo 1 > events/sched/enable
+ # echo 1 > snapshot
+ # cat snapshot
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 71/71   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [005] d...  2440.603828: sched_switch: prev_comm=swapper/5 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2242 next_prio=120
+           sleep-2242  [005] d...  2440.603846: sched_switch: prev_comm=snapshot-test-2 prev_pid=2242 prev_prio=120 prev_state=R ==> next_comm=kworker/5:1 next_pid=60 next_prio=120
+[...]
+          <idle>-0     [002] d...  2440.707230: sched_switch: prev_comm=swapper/2 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2229 next_prio=120
+
+ # cat trace
+# tracer: nop
+#
+# entries-in-buffer/entries-written: 77/77   #P:8
+#
+#                              _-----=> irqs-off
+#                             / _----=> need-resched
+#                            | / _---=> hardirq/softirq
+#                            || / _--=> preempt-depth
+#                            ||| /     delay
+#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
+#              | |       |   ||||       |         |
+          <idle>-0     [007] d...  2440.707395: sched_switch: prev_comm=swapper/7 prev_pid=0 prev_prio=120 prev_state=R ==> next_comm=snapshot-test-2 next_pid=2243 next_prio=120
+ snapshot-test-2-2229  [002] d...  2440.707438: sched_switch: prev_comm=snapshot-test-2 prev_pid=2229 prev_prio=120 prev_state=S ==> next_comm=swapper/2 next_pid=0 next_prio=120
+[...]
+
+
+If you try to use this snapshot feature when current tracer is
+one of the latency tracers, you will get the following results.
+
+ # echo wakeup > current_tracer
+ # echo 1 > snapshot
+bash: echo: write error: Device or resource busy
+ # cat snapshot
+cat: snapshot: Device or resource busy
+
 -----------
 
 More details can be found in the source code, in the