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Commit f7355a5e authored by Ingo Molnar's avatar Ingo Molnar
Browse files

Merge branch 'tip/perf/core' of... 

Merge branch 'tip/perf/core' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

 into perf/core

Pull tracing updated from Steve Rostedt.

Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parents 9c4c5fd9 d840f718

Documentation/trace/ftrace.txt

+83 −0
Original line number Diff line number Diff line
@@ -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

include/linux/ftrace_event.h

+3 −0
Original line number Diff line number Diff line
@@ -83,6 +83,9 @@ struct trace_iterator { 
	long			idx;



	cpumask_var_t		started;



	/* it's true when current open file is snapshot */

	bool			snapshot;

};



enum trace_iter_flags {

include/linux/ring_buffer.h

+1 −0
Original line number Diff line number Diff line
@@ -167,6 +167,7 @@ unsigned long ring_buffer_entries_cpu(struct ring_buffer *buffer, int cpu); 
unsigned long ring_buffer_overrun_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_commit_overrun_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu);

unsigned long ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu);



u64 ring_buffer_time_stamp(struct ring_buffer *buffer, int cpu);

void ring_buffer_normalize_time_stamp(struct ring_buffer *buffer,

kernel/trace/Kconfig

+10 −0
Original line number Diff line number Diff line
@@ -253,6 +253,16 @@ config FTRACE_SYSCALLS 
	help

	  Basic tracer to catch the syscall entry and exit events.



config TRACER_SNAPSHOT

	bool "Create a snapshot trace buffer"

	select TRACER_MAX_TRACE

	help

	  Allow tracing users to take snapshot of the current buffer using the

	  ftrace interface, e.g.:



	      echo 1 > /sys/kernel/debug/tracing/snapshot

	      cat snapshot



config TRACE_BRANCH_PROFILING

	bool

	select GENERIC_TRACER

kernel/trace/ring_buffer.c

+18 −0
Original line number Diff line number Diff line
@@ -3102,6 +3102,24 @@ ring_buffer_dropped_events_cpu(struct ring_buffer *buffer, int cpu) 
}

EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);



/**

 * ring_buffer_read_events_cpu - get the number of events successfully read

 * @buffer: The ring buffer

 * @cpu: The per CPU buffer to get the number of events read

 */

unsigned long

ring_buffer_read_events_cpu(struct ring_buffer *buffer, int cpu)

{

	struct ring_buffer_per_cpu *cpu_buffer;



	if (!cpumask_test_cpu(cpu, buffer->cpumask))

		return 0;



	cpu_buffer = buffer->buffers[cpu];

	return cpu_buffer->read;

}

EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);



/**

 * ring_buffer_entries - get the number of entries in a buffer

 * @buffer: The ring buffer