ftrace: display start of CPU buffer in trace output (a309720c) · Commits · 戴 / test

Impact: change in trace output Because the trace buffers are per cpu ring buffers, the start of the trace can be confusing. If one CPU is very active at the end of the trace, its history will not go as far back as the other CPU traces. This means that output for a particular CPU may not appear for the first part of a trace. To help annotate what is happening, and to prevent any more confusion, this patch adds a line that annotates the start of a CPU buffer output. For example: automount-3495 [001] 184.596443: dnotify_parent <-vfs_write [...] automount-3495 [001] 184.596449: dput <-path_put automount-3496 [002] 184.596450: down_read_trylock <-do_page_fault [...] sshd-3497 [001] 184.597069: up_read <-do_page_fault <idle>-0 [000] 184.597074: __exit_idle <-exit_idle [...] automount-3496 [002] 184.597257: filemap_fault <-__do_fault <idle>-0 [003] 184.597261: exit_idle <-smp_apic_timer_interrupt Note, parsers of a trace output should always ignore any lines that start with a '#'. Signed-off-by:

Steven Rostedt <srostedt@redhat.com> Signed-off-by:

Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

+19 −0

Original line number	Diff line number	Diff line
		@@ -1478,6 +1478,17 @@ void trace_seq_print_cont(struct trace_seq s, struct trace_iterator iter)
		trace_seq_putc(s, '\n');
		}

		static void test_cpu_buff_start(struct trace_iterator *iter)
		{
		struct trace_seq *s = &iter->seq;

		if (cpu_isset(iter->cpu, iter->started))
		return;

		cpu_set(iter->cpu, iter->started);
		trace_seq_printf(s, "##### CPU %u buffer started ####\n", iter->cpu);
		}

		static enum print_line_t
		print_lat_fmt(struct trace_iterator *iter, unsigned int trace_idx, int cpu)
		{
		@@ -1497,6 +1508,8 @@ print_lat_fmt(struct trace_iterator *iter, unsigned int trace_idx, int cpu)
		if (entry->type == TRACE_CONT)
		return TRACE_TYPE_HANDLED;

		test_cpu_buff_start(iter);

		next_entry = find_next_entry(iter, NULL, &next_ts);
		if (!next_entry)
		next_ts = iter->ts;
		@@ -1612,6 +1625,8 @@ static enum print_line_t print_trace_fmt(struct trace_iterator *iter)
		if (entry->type == TRACE_CONT)
		return TRACE_TYPE_HANDLED;

		test_cpu_buff_start(iter);

		comm = trace_find_cmdline(iter->ent->pid);

		t = ns2usecs(iter->ts);
		@@ -2631,6 +2646,10 @@ static int tracing_open_pipe(struct inode inode, struct file filp)
		return -ENOMEM;

		mutex_lock(&trace_types_lock);

		/* trace pipe does not show start of buffer */
		cpus_setall(iter->started);

		iter->tr = &global_trace;
		iter->trace = current_trace;
		filp->private_data = iter;

kernel/trace/trace.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -277,6 +277,8 @@ struct trace_iterator {
		unsigned long iter_flags;
		loff_t pos;
		long idx;

		cpumask_t started;
		};

		int tracing_is_enabled(void);

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