[PATCH v8 34/37] tracing: Add a clock attribute for hist triggers

Tom Zanussi
2017-12-21T16:05:13Z

The default clock if timestamps are used in a histogram is "global".
If timestamps aren't used, the clock is irrelevant.

Use the "clock=" param only if you want to override the default
"global" clock for a histogram with timestamps.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Rajvi Jingar <rajvi.jingar@intel.com>
---
Documentation/trace/histogram.txt | 11 +++++++++-
kernel/trace/trace_events_hist.c | 42 ++++++++++++++++++++++++++++++++++++---
2 files changed, 49 insertions(+), 4 deletions(-)

diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt
index df08882..6e05510 100644
--- a/Documentation/trace/histogram.txt
+++ b/Documentation/trace/histogram.txt
@@ -1671,7 +1671,16 @@ features have been added to the hist trigger support:
it is in units of nanoseconds; appending '.usecs' to a
common_timestamp field changes the units to microseconds.

-These features are decribed in more detail in the following sections.
+A note on inter-event timestamps: If common_timestamp is used in a
+histogram, the trace buffer is automatically switched over to using
+absolute timestamps and the "global" trace clock, in order to avoid
+bogus timestamp differences with other clocks that aren't coherent
+across CPUs. This can be overridden by specifying one of the other
+trace clocks instead, using the "clock=XXX" hist trigger attribute,
+where XXX is any of the clocks listed in the tracing/trace_clock
+pseudo-file.
+
+These features are described in more detail in the following sections.

2.2.1 Histogram Variables
-------------------------
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 2481cce..9a462a9 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -242,6 +242,7 @@ struct hist_trigger_attrs {
char *vals_str;
char *sort_key_str;
char *name;
+ char *clock;
bool pause;
bool cont;
bool clear;
@@ -1780,6 +1781,7 @@ static void destroy_hist_trigger_attrs(struct hist_trigger_attrs *attrs)
kfree(attrs->sort_key_str);
kfree(attrs->keys_str);
kfree(attrs->vals_str);
+ kfree(attrs->clock);
kfree(attrs);
}

@@ -1835,6 +1837,19 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
ret = -ENOMEM;
goto out;
}
+ } else if (strncmp(str, "clock=", strlen("clock=")) == 0) {
+ strsep(&str, "=");
+ if (!str) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ str = strstrip(str);
+ attrs->clock = kstrdup(str, GFP_KERNEL);
+ if (!attrs->clock) {
+ ret = -ENOMEM;
+ goto out;
+ }
} else if (strncmp(str, "size=", strlen("size=")) == 0) {
int map_bits = parse_map_size(str);

@@ -1899,6 +1914,14 @@ static struct hist_trigger_attrs *parse_hist_trigger_attrs(char *trigger_str)
goto free;
}

+ if (!attrs->clock) {
+ attrs->clock = kstrdup("global", GFP_KERNEL);
+ if (!attrs->clock) {
+ ret = -ENOMEM;
+ goto free;
+ }
+ }
+
return attrs;
free:
destroy_hist_trigger_attrs(attrs);
@@ -4923,6 +4946,8 @@ static int event_hist_trigger_print(struct seq_file *m,
seq_puts(m, ".descending");
}
seq_printf(m, ":size=%u", (1 << hist_data->map->map_bits));
+ if (hist_data->enable_timestamps)
+ seq_printf(m, ":clock=%s", hist_data->attrs->clock);

print_actions_spec(m, hist_data);

@@ -5190,7 +5215,6 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
data->paused = true;

if (named_data) {
- destroy_hist_data(data->private_data);
data->private_data = named_data->private_data;
set_named_trigger_data(data, named_data);
data->ops = &event_hist_trigger_named_ops;
@@ -5202,10 +5226,22 @@ static int hist_register_trigger(char *glob, struct event_trigger_ops *ops,
goto out;
}

- ret++;
+ if (hist_data->enable_timestamps) {
+ char *clock = hist_data->attrs->clock;
+
+ ret = tracing_set_clock(file->tr, hist_data->attrs->clock);
+ if (ret) {
+ hist_err("Couldn't set trace_clock: ", clock);
+ goto out;
+ }

- if (hist_data->enable_timestamps)
tracing_set_time_stamp_abs(file->tr, true);
+ }
+
+ if (named_data)
+ destroy_hist_data(hist_data);
+
+ ret++;
out:
return ret;
}
--
1.9.3