trace: better manage the context info for events

Impact: make trace_event more convenient for tracers

All tracers (for the moment) that use the struct trace_event want to
have the context info printed before their own output: the pid/cmdline,
cpu, and timestamp.

But some other tracers that want to implement their trace_event
callbacks will not necessary need these information or they may want to
format them as they want.

This patch adds a new default-enabled trace option:
TRACE_ITER_CONTEXT_INFO When disabled through:

echo nocontext-info > /debugfs/tracing/trace_options

The pid, cpu and timestamps headers will not be printed.

IE with the sched_switch tracer with context-info (default):

     bash-2935 [001] 100.356561: 2935:120:S ==> [001]  0:140:R <idle>
   <idle>-0    [000] 100.412804:    0:140:R   + [000] 11:115:S events/0
   <idle>-0    [000] 100.412816:    0:140:R ==> [000] 11:115:R events/0
 events/0-11   [000] 100.412829:   11:115:S ==> [000]  0:140:R <idle>

Without context-info:

 2935:120:S ==> [001]  0:140:R <idle>
    0:140:R   + [000] 11:115:S events/0
    0:140:R ==> [000] 11:115:R events/0
   11:115:S ==> [000]  0:140:R <idle>

A tracer can disable it at runtime by clearing the bit
TRACE_ITER_CONTEXT_INFO in trace_flags.

The print routines were renamed to trace_print_context and
trace_print_lat_context, so that they can be used by tracers if they
want to use them for one of the trace_event callbacks.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 107 insertions, 0 deletions

diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 1a4e144a9f8..a5752d4d3c3 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -286,6 +286,113 @@ seq_print_ip_sym(struct trace_seq *s, unsigned long ip, unsigned long sym_flags)
 	return ret;
 }
 
+static void
+lat_print_generic(struct trace_seq *s, struct trace_entry *entry, int cpu)
+{
+	int hardirq, softirq;
+	char *comm;
+
+	comm = trace_find_cmdline(entry->pid);
+
+	trace_seq_printf(s, "%8.8s-%-5d ", comm, entry->pid);
+	trace_seq_printf(s, "%3d", cpu);
+	trace_seq_printf(s, "%c%c",
+			(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :
+			 (entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' : '.',
+			((entry->flags & TRACE_FLAG_NEED_RESCHED) ? 'N' : '.'));
+
+	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;
+	softirq = entry->flags & TRACE_FLAG_SOFTIRQ;
+	if (hardirq && softirq) {
+		trace_seq_putc(s, 'H');
+	} else {
+		if (hardirq) {
+			trace_seq_putc(s, 'h');
+		} else {
+			if (softirq)
+				trace_seq_putc(s, 's');
+			else
+				trace_seq_putc(s, '.');
+		}
+	}
+
+	if (entry->preempt_count)
+		trace_seq_printf(s, "%x", entry->preempt_count);
+	else
+		trace_seq_puts(s, ".");
+}
+
+static unsigned long preempt_mark_thresh = 100;
+
+static void
+lat_print_timestamp(struct trace_seq *s, u64 abs_usecs,
+		    unsigned long rel_usecs)
+{
+	trace_seq_printf(s, " %4lldus", abs_usecs);
+	if (rel_usecs > preempt_mark_thresh)
+		trace_seq_puts(s, "!: ");
+	else if (rel_usecs > 1)
+		trace_seq_puts(s, "+: ");
+	else
+		trace_seq_puts(s, " : ");
+}
+
+int trace_print_context(struct trace_iterator *iter)
+{
+	struct trace_seq *s = &iter->seq;
+	struct trace_entry *entry = iter->ent;
+	char *comm = trace_find_cmdline(entry->pid);
+	unsigned long long t = ns2usecs(iter->ts);
+	unsigned long usec_rem = do_div(t, USEC_PER_SEC);
+	unsigned long secs = (unsigned long)t;
+
+	if (!trace_seq_printf(s, "%16s-%-5d ", comm, entry->pid))
+		goto partial;
+	if (!trace_seq_printf(s, "[%03d] ", entry->cpu))
+		goto partial;
+	if (!trace_seq_printf(s, "%5lu.%06lu: ", secs, usec_rem))
+		goto partial;
+
+	return 0;
+
+partial:
+	return TRACE_TYPE_PARTIAL_LINE;
+}
+
+int trace_print_lat_context(struct trace_iterator *iter)
+{
+	u64 next_ts;
+	struct trace_seq *s = &iter->seq;
+	struct trace_entry *entry = iter->ent,
+			   *next_entry = trace_find_next_entry(iter, NULL,
+							       &next_ts);
+	unsigned long verbose = (trace_flags & TRACE_ITER_VERBOSE);
+	unsigned long abs_usecs = ns2usecs(iter->ts - iter->tr->time_start);
+	unsigned long rel_usecs;
+
+	if (!next_entry)
+		next_ts = iter->ts;
+	rel_usecs = ns2usecs(next_ts - iter->ts);
+
+	if (verbose) {
+		char *comm = trace_find_cmdline(entry->pid);
+		trace_seq_printf(s, "%16s %5d %3d %d %08x %08lx [%08lx]"
+				 " %ld.%03ldms (+%ld.%03ldms): ",
+				 comm,
+				 entry->pid, entry->cpu, entry->flags,
+				 entry->preempt_count, iter->idx,
+				 ns2usecs(iter->ts),
+				 abs_usecs/1000,
+				 abs_usecs % 1000, rel_usecs/1000,
+				 rel_usecs % 1000);
+	} else {
+		lat_print_generic(s, entry, entry->cpu);
+		lat_print_timestamp(s, abs_usecs, rel_usecs);
+	}
+
+	return 0;
+}
+
 static const char state_to_char[] = TASK_STATE_TO_CHAR_STR;
 
 static int task_state_char(unsigned long state)