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Subject[PATCH v2 39/40] tracing: Add a clock attribute for hist triggers
Date
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>
---
Documentation/trace/events.txt | 9 +++++++++
kernel/trace/trace_events_hist.c | 34 +++++++++++++++++++++++++++++++---
2 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/Documentation/trace/events.txt b/Documentation/trace/events.txt
index 7ee720b..9bd4b7f 100644
--- a/Documentation/trace/events.txt
+++ b/Documentation/trace/events.txt
@@ -2173,6 +2173,15 @@ features have been added to the hist trigger support:
default it is in units of nanoseconds; appending '.usecs' to a
common_timestamp field changes the units to microseconds.

+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 decribed in more detail in the following sections.

6.3.1 Histogram Variables
diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 655b731..eb77eee 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -241,6 +241,7 @@ struct hist_trigger_attrs {
char *vals_str;
char *sort_key_str;
char *name;
+ char *clock;
bool pause;
bool cont;
bool clear;
@@ -1701,6 +1702,7 @@ 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);
}

@@ -1740,7 +1742,16 @@ static int parse_assignment(char *str, struct hist_trigger_attrs *attrs)
attrs->sort_key_str = kstrdup(str, GFP_KERNEL);
else if (strncmp(str, "name=", strlen("name=")) == 0)
attrs->name = kstrdup(str, GFP_KERNEL);
- else if (strncmp(str, "size=", strlen("size=")) == 0) {
+ 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);
+ } else if (strncmp(str, "size=", strlen("size=")) == 0) {
int map_bits = parse_map_size(str);

if (map_bits < 0) {
@@ -1803,6 +1814,12 @@ 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)
+ goto free;
+ }
+
return attrs;
free:
destroy_hist_trigger_attrs(attrs);
@@ -4644,6 +4661,8 @@ 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);

@@ -4907,10 +4926,19 @@ 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);
+ }
+
+ ret++;
out:
return ret;
}
--
1.9.3
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