[PATCH 26/32] tracing: Make duplicate count from tracing_map available

Tom Zanussi
2017-06-26T22:51:40Z

Though extremely rare, there can be duplicate entries in the tracing
map. This isn't normally a problem, as the sorting code makes this
transparent by merging them during the sort.

It's useful to know however, as a check on that assumption - if a
non-zero duplicate count is seen more than rarely, it might indicate
an unexpected change to the algorithm, or a pathological data set.

Add an extra param to tracing_map_sort_entries() and use it to display
the value in the hist trigger output.

Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
---
kernel/trace/trace_events_hist.c | 14 ++++++++------
kernel/trace/tracing_map.c | 12 +++++++++---
kernel/trace/tracing_map.h | 3 ++-
3 files changed, 19 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 53a0634..ab94e2a 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -4011,7 +4011,8 @@ static void hist_trigger_stacktrace_print(struct seq_file *m,
}

static int print_entries(struct seq_file *m,
- struct hist_trigger_data *hist_data)
+ struct hist_trigger_data *hist_data,
+ unsigned int *n_dups)
{
struct tracing_map_sort_entry **sort_entries = NULL;
struct tracing_map *map = hist_data->map;
@@ -4019,7 +4020,7 @@ static int print_entries(struct seq_file *m,

n_entries = tracing_map_sort_entries(map, hist_data->sort_keys,
hist_data->n_sort_keys,
- &sort_entries);
+ &sort_entries, n_dups);
if (n_entries < 0)
return n_entries;

@@ -4038,6 +4039,7 @@ static void hist_trigger_show(struct seq_file *m,
{
struct hist_trigger_data *hist_data;
int n_entries, ret = 0;
+ unsigned int n_dups;

if (n > 0)
seq_puts(m, "\n\n");
@@ -4047,15 +4049,15 @@ static void hist_trigger_show(struct seq_file *m,
seq_puts(m, "#\n\n");

hist_data = data->private_data;
- n_entries = print_entries(m, hist_data);
+ n_entries = print_entries(m, hist_data, &n_dups);
if (n_entries < 0) {
ret = n_entries;
n_entries = 0;
}

- seq_printf(m, "\nTotals:\n Hits: %llu\n Entries: %u\n Dropped: %llu\n",
- (u64)atomic64_read(&hist_data->map->hits),
- n_entries, (u64)atomic64_read(&hist_data->map->drops));
+ seq_printf(m, "\nTotals:\n Hits: %llu\n Entries: %u\n Dropped: %llu\n Duplicates: %u\n",
+ (u64)atomic64_read(&hist_data->map->hits), n_entries,
+ (u64)atomic64_read(&hist_data->map->drops), n_dups);
}

static int hist_show(struct seq_file *m, void *v)
diff --git a/kernel/trace/tracing_map.c b/kernel/trace/tracing_map.c
index f987069..9ed04b6 100644
--- a/kernel/trace/tracing_map.c
+++ b/kernel/trace/tracing_map.c
@@ -1084,6 +1084,7 @@ static void sort_secondary(struct tracing_map *map,
* @map: The tracing_map
* @sort_key: The sort key to use for sorting
* @sort_entries: outval: pointer to allocated and sorted array of entries
+ * @n_dups: outval: pointer to variable receiving a count of duplicates found
*
* tracing_map_sort_entries() sorts the current set of entries in the
* map and returns the list of tracing_map_sort_entries containing
@@ -1100,13 +1101,16 @@ static void sort_secondary(struct tracing_map *map,
* The client should not hold on to the returned array but should use
* it and call tracing_map_destroy_sort_entries() when done.
*
- * Return: the number of sort_entries in the struct tracing_map_sort_entry
- * array, negative on error
+ * Return: the number of sort_entries in the struct
+ * tracing_map_sort_entry array, negative on error. If n_dups is
+ * non-NULL, it will receive the number of duplicate entries found
+ * (and merged) during the sort.
*/
int tracing_map_sort_entries(struct tracing_map *map,
struct tracing_map_sort_key *sort_keys,
unsigned int n_sort_keys,
- struct tracing_map_sort_entry ***sort_entries)
+ struct tracing_map_sort_entry ***sort_entries,
+ unsigned int *n_dups)
{
int (*cmp_entries_fn)(const struct tracing_map_sort_entry **,
const struct tracing_map_sort_entry **);
@@ -1147,6 +1151,8 @@ int tracing_map_sort_entries(struct tracing_map *map,
if (ret < 0)
goto free;
n_entries -= ret;
+ if (n_dups)
+ *n_dups = ret;

if (is_key(map, sort_keys[0].field_idx))
cmp_entries_fn = cmp_entries_key;
diff --git a/kernel/trace/tracing_map.h b/kernel/trace/tracing_map.h
index 303bc4f..a44cc0c 100644
--- a/kernel/trace/tracing_map.h
+++ b/kernel/trace/tracing_map.h
@@ -286,7 +286,8 @@ extern void tracing_map_set_field_descr(struct tracing_map *map,
tracing_map_sort_entries(struct tracing_map *map,
struct tracing_map_sort_key *sort_keys,
unsigned int n_sort_keys,
- struct tracing_map_sort_entry ***sort_entries);
+ struct tracing_map_sort_entry ***sort_entries,
+ unsigned int *n_dups);

extern void
tracing_map_destroy_sort_entries(struct tracing_map_sort_entry **entries,
--
1.9.3