tracing: updates

Ingo,

Please pull the latest tip/perf/core tree, which can be found at:

git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git
tip/perf/core

Head SHA1: 39eaf7ef884dcc44f7ff1bac803ca2a1dcf43544

Steven Rostedt (2):
tracing: Add irq, preempt-count and need resched info to default trace output
tracing: Add entries in buffer and total entries to default output header

----

 kernel/trace/trace.c        |   90 ++++++++++++++++++++++++++++++------------
 kernel/trace/trace.h        |    1 +
 kernel/trace/trace_output.c |   16 +++++++-
 3 files changed, 79 insertions(+), 28 deletions(-)

From: Steven Rostedt <[email protected]>

People keep asking how to get the preempt count, irq, and need resched info and we keep telling them to enable the latency format. Some developers think that traces without this info is completely useless, and for a lot of tasks it is useless.

The first option was to enable the latency trace as the default format, but the header for the latency format is pretty useless for most tracers and it also does the timestamp in straight microseconds from the time the trace started. This is sometimes more difficult to read as the default trace is seconds from the start of boot up.

Latency format:

# tracer: nop
#

 # nop latency trace v1.1.5 on 3.2.0-rc1-test+
 # --------------------------------------------------------------------
 # latency: 0 us, #159771/64234230, CPU#1 | (M:preempt VP:0, KP:0, SP:0 HP:0 #P:4)
 #    -----------------
 #    | task: -0 (uid:0 nice:0 policy:0 rt_prio:0)
 #    -----------------
 #
 #                  _------=> CPU#
 #                 / _-----=> irqs-off
 #                | / _----=> need-resched
 #                || / _---=> hardirq/softirq
 #                ||| / _--=> preempt-depth
 #                |||| /     delay
 #  cmd     pid   ||||| time  |   caller
 #     \   /      |||||  \    |   /
 migratio-6       0...2 41778231us+: rcu_note_context_switch <-__schedule
 migratio-6       0...2 41778233us : trace_rcu_utilization <-rcu_note_context_switch
 migratio-6       0...2 41778235us+: rcu_sched_qs <-rcu_note_context_switch
 migratio-6       0d..2 41778236us+: rcu_preempt_qs <-rcu_note_context_switch
 migratio-6       0...2 41778238us : trace_rcu_utilization <-rcu_note_context_switch
 migratio-6       0...2 41778239us+: debug_lockdep_rcu_enabled <-__schedule

default format:

# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |

      migration/0-6     [000]    50.025810: rcu_note_context_switch <-__schedule
      migration/0-6     [000]    50.025812: trace_rcu_utilization <-rcu_note_context_switch
      migration/0-6     [000]    50.025813: rcu_sched_qs <-rcu_note_context_switch
      migration/0-6     [000]    50.025815: rcu_preempt_qs <-rcu_note_context_switch
      migration/0-6     [000]    50.025817: trace_rcu_utilization <-rcu_note_context_switch
      migration/0-6     [000]    50.025818: debug_lockdep_rcu_enabled <-__schedule
      migration/0-6     [000]    50.025820: debug_lockdep_rcu_enabled <-__schedule

The latency format header has latency information that is pretty meaningless for most tracers. Although some of the header is useful, and we can add that later to the default format as well.

What is really useful with the latency format is the irqs-off, need-resched hard/softirq context and the preempt count.

This commit adds the option irq-info which is on by default that adds this information:

# tracer: nop
#
# _-----=> irqs-off
# / _----=> need-resched

 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |
           <idle>-0     [000] d..2    49.309305: cpuidle_get_driver <-cpuidle_idle_call
           <idle>-0     [000] d..2    49.309307: mwait_idle <-cpu_idle
           <idle>-0     [000] d..2    49.309309: need_resched <-mwait_idle
           <idle>-0     [000] d..2    49.309310: test_ti_thread_flag <-need_resched
           <idle>-0     [000] d..2    49.309312: trace_power_start.constprop.13 <-mwait_idle
           <idle>-0     [000] d..2    49.309313: trace_cpu_idle <-mwait_idle
           <idle>-0     [000] d..2    49.309315: need_resched <-mwait_idle

If a user wants the old format, they can disable the 'irq-info' option:

# tracer: nop
#
# TASK-PID CPU# TIMESTAMP FUNCTION
# | | | | |

           <idle>-0     [000]     49.309305: cpuidle_get_driver <-cpuidle_idle_call
           <idle>-0     [000]     49.309307: mwait_idle <-cpu_idle
           <idle>-0     [000]     49.309309: need_resched <-mwait_idle
           <idle>-0     [000]     49.309310: test_ti_thread_flag <-need_resched
           <idle>-0     [000]     49.309312: trace_power_start.constprop.13 <-mwait_idle
           <idle>-0     [000]     49.309313: trace_cpu_idle <-mwait_idle
           <idle>-0     [000]     49.309315: need_resched <-mwait_idle

---
 kernel/trace/trace.c        |   24 ++++++++++++++++++++----
 kernel/trace/trace.h        |    1 +
 kernel/trace/trace_output.c |   16 ++++++++++++++--
 3 files changed, 35 insertions(+), 6 deletions(-)

index 9e158cc..fa5cee6 100644
@@ -338,7 +338,8 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
 /* trace_flags holds trace_options default values */
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT | TRACE_ITER_PRINTK |
 	TRACE_ITER_ANNOTATE | TRACE_ITER_CONTEXT_INFO | TRACE_ITER_SLEEP_TIME |
-	TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE;
+	TRACE_ITER_GRAPH_TIME | TRACE_ITER_RECORD_CMD | TRACE_ITER_OVERWRITE |
+	TRACE_ITER_IRQ_INFO;
 
 static int trace_stop_count;
 static DEFINE_RAW_SPINLOCK(tracing_start_lock);

@@ -426,6 +427,7 @@ static const char *trace_options[] = {
 	"record-cmd",
 	"overwrite",
 	"disable_on_free",
+	"irq-info",
 	NULL
 };
 

@@ -1857,10 +1859,20 @@ static void print_lat_help_header(struct seq_file *m)
 
 static void print_func_help_header(struct seq_file *m)
 {
-	seq_puts(m, "#           TASK-PID    CPU#    TIMESTAMP  FUNCTION\n");
+	seq_puts(m, "#           TASK-PID   CPU#      TIMESTAMP  FUNCTION\n");
 	seq_puts(m, "#              | |       |          |         |\n");
 }
 
+static void print_func_help_header_irq(struct seq_file *m)
+{
+	seq_puts(m, "#                              _-----=> irqs-off\n");
+	seq_puts(m, "#                             / _----=> need-resched\n");
+	seq_puts(m, "#                            | / _---=> hardirq/softirq\n");
+	seq_puts(m, "#                            || / _--=> preempt-depth\n");
+	seq_puts(m, "#                            ||| /     delay\n");
+	seq_puts(m, "#           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION\n");
+	seq_puts(m, "#              | |       |   ||||       |         |\n");
+}
 
 void
 print_trace_header(struct seq_file *m, struct trace_iterator *iter)

@@ -2170,8 +2182,12 @@ void trace_default_header(struct seq_file *m)
 		if (!(trace_flags & TRACE_ITER_VERBOSE))
 			print_lat_help_header(m);
 	} else {
-		if (!(trace_flags & TRACE_ITER_VERBOSE))
-			print_func_help_header(m);
+		if (!(trace_flags & TRACE_ITER_VERBOSE)) {
+			if (trace_flags & TRACE_ITER_IRQ_INFO)
+				print_func_help_header_irq(m);
+			else
+				print_func_help_header(m);
+		}
 	}
 }
 

index f8ec229..2c26574 100644
@@ -655,6 +655,7 @@ enum trace_iterator_flags {
 	TRACE_ITER_RECORD_CMD		= 0x100000,
 	TRACE_ITER_OVERWRITE		= 0x200000,
 	TRACE_ITER_STOP_ON_FREE		= 0x400000,
+	TRACE_ITER_IRQ_INFO		= 0x800000,
 };
 
 /*

index 5199930..0d6ff355 100644
@@ -627,11 +627,23 @@ int trace_print_context(struct trace_iterator *iter)
 	unsigned long usec_rem = do_div(t, USEC_PER_SEC);
 	unsigned long secs = (unsigned long)t;
 	char comm[TASK_COMM_LEN];
+	int ret;
 
 	trace_find_cmdline(entry->pid, comm);
 
-	return trace_seq_printf(s, "%16s-%-5d [%03d] %5lu.%06lu: ",
-				comm, entry->pid, iter->cpu, secs, usec_rem);
+	ret = trace_seq_printf(s, "%16s-%-5d [%03d] ",
+			       comm, entry->pid, iter->cpu);
+	if (!ret)
+		return 0;
+
+	if (trace_flags & TRACE_ITER_IRQ_INFO) {
+		ret = trace_print_lat_fmt(s, entry);
+		if (!ret)
+			return 0;
+	}
+
+	return trace_seq_printf(s, " %5lu.%06lu: ",
+				secs, usec_rem);
 }
 
 int trace_print_lat_context(struct trace_iterator *iter)

1.7.7.3

From: Steven Rostedt <[email protected]>

Knowing the number of event entries in the ring buffer compared to the total number that were written is useful information. The latency format gives this information and there's no reason that the default format does not.

This information is now added to the default header, along with the number of online CPUs:

# tracer: nop
#
# entries-in-buffer/entries-written: 159836/64690869 #P:4
#
# _-----=> irqs-off
# / _----=> need-resched

 #                            | / _---=> hardirq/softirq
 #                            || / _--=> preempt-depth
 #                            ||| /     delay
 #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
 #              | |       |   ||||       |         |
           <idle>-0     [000] ...2    49.442971: local_touch_nmi <-cpu_idle
           <idle>-0     [000] d..2    49.442973: enter_idle <-cpu_idle
           <idle>-0     [000] d..2    49.442974: atomic_notifier_call_chain <-enter_idle
           <idle>-0     [000] d..2    49.442976: __atomic_notifier_call_chain <-atomic_notifier

The above shows that the trace contains 159836 entries, but 64690869 were written. One could figure out that there were 64531033 entries that were dropped.

---
 kernel/trace/trace.c |   72 ++++++++++++++++++++++++++++++++-----------------
 1 files changed, 47 insertions(+), 25 deletions(-)

index fa5cee6..7392070 100644
@@ -1845,6 +1845,33 @@ static void s_stop(struct seq_file *m, void *p)
 	trace_event_read_unlock();
 }
 
+static void
+get_total_entries(struct trace_array *tr, unsigned long *total, unsigned long *entries)
+{
+	unsigned long count;
+	int cpu;
+
+	*total = 0;
+	*entries = 0;
+
+	for_each_tracing_cpu(cpu) {
+		count = ring_buffer_entries_cpu(tr->buffer, cpu);
+		/*
+		 * If this buffer has skipped entries, then we hold all
+		 * entries for the trace and we need to ignore the
+		 * ones before the time stamp.
+		 */
+		if (tr->data[cpu]->skipped_entries) {
+			count -= tr->data[cpu]->skipped_entries;
+			/* total is the same as the entries */
+			*total += count;
+		} else
+			*total += count +
+				ring_buffer_overrun_cpu(tr->buffer, cpu);
+		*entries += count;
+	}
+}
+
 static void print_lat_help_header(struct seq_file *m)
 {
 	seq_puts(m, "#                  _------=> CPU#            \n");

@@ -1857,14 +1884,27 @@ static void print_lat_help_header(struct seq_file *m)
 	seq_puts(m, "#     \\   /      |||||  \\    |   /           \n");
 }
 
-static void print_func_help_header(struct seq_file *m)
+static void print_event_info(struct trace_array *tr, struct seq_file *m)
 {
+	unsigned long total;
+	unsigned long entries;
+
+	get_total_entries(tr, &total, &entries);
+	seq_printf(m, "# entries-in-buffer/entries-written: %lu/%lu   #P:%d\n",
+		   entries, total, num_online_cpus());
+	seq_puts(m, "#\n");
+}
+
+static void print_func_help_header(struct trace_array *tr, struct seq_file *m)
+{
+	print_event_info(tr, m);
 	seq_puts(m, "#           TASK-PID   CPU#      TIMESTAMP  FUNCTION\n");
 	seq_puts(m, "#              | |       |          |         |\n");
 }
 
-static void print_func_help_header_irq(struct seq_file *m)
+static void print_func_help_header_irq(struct trace_array *tr, struct seq_file *m)
 {
+	print_event_info(tr, m);
 	seq_puts(m, "#                              _-----=> irqs-off\n");
 	seq_puts(m, "#                             / _----=> need-resched\n");
 	seq_puts(m, "#                            | / _---=> hardirq/softirq\n");

@@ -1881,32 +1921,14 @@ print_trace_header(struct seq_file *m, struct trace_iterator *iter)
 	struct trace_array *tr = iter->tr;
 	struct trace_array_cpu *data = tr->data[tr->cpu];
 	struct tracer *type = current_trace;
-	unsigned long entries = 0;
-	unsigned long total = 0;
-	unsigned long count;
+	unsigned long entries;
+	unsigned long total;
 	const char *name = "preemption";
-	int cpu;
 
 	if (type)
 		name = type->name;
 
-
-	for_each_tracing_cpu(cpu) {
-		count = ring_buffer_entries_cpu(tr->buffer, cpu);
-		/*
-		 * If this buffer has skipped entries, then we hold all
-		 * entries for the trace and we need to ignore the
-		 * ones before the time stamp.
-		 */
-		if (tr->data[cpu]->skipped_entries) {
-			count -= tr->data[cpu]->skipped_entries;
-			/* total is the same as the entries */
-			total += count;
-		} else
-			total += count +
-				ring_buffer_overrun_cpu(tr->buffer, cpu);
-		entries += count;
-	}
+	get_total_entries(tr, &total, &entries);
 
 	seq_printf(m, "# %s latency trace v1.1.5 on %s\n",
 		   name, UTS_RELEASE);

@@ -2184,9 +2206,9 @@ void trace_default_header(struct seq_file *m)
 	} else {
 		if (!(trace_flags & TRACE_ITER_VERBOSE)) {
 			if (trace_flags & TRACE_ITER_IRQ_INFO)
-				print_func_help_header_irq(m);
+				print_func_help_header_irq(iter->tr, m);
 			else
-				print_func_help_header(m);
+				print_func_help_header(iter->tr, m);
 		}
 	}
 }

1.7.7.3