Merge branch 'tip/perf/core' of... (f7355a5e) · Commits · EulixOS / Software / Kernel

Documentation/trace/ftrace.txt

+83 −0

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		@@ -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

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		@@ -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

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		@@ -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

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		@@ -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

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		@@ -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