[RFD 2/5] tracing: Add support to sort on the key

[Daniel Wagner <daniel.wagner@bmw-carit.de>]

The hist patch allows sorting on values only. By allowing to
sort also on the key we can do something like this:

'hist:key=latency:val=hitcount:sort=latency'

latency:         16 hitcount:          3
latency:         17 hitcount:        171
latency:         18 hitcount:        626
latency:         19 hitcount:        594
latency:         20 hitcount:        306
latency:         21 hitcount:        214
latency:         22 hitcount:        232
latency:         23 hitcount:        283
latency:         24 hitcount:        235
latency:         25 hitcount:        105
latency:         26 hitcount:         54
latency:         27 hitcount:         79
latency:         28 hitcount:        214
latency:         29 hitcount:        895
latency:         30 hitcount:       1400
latency:         31 hitcount:        774
latency:         32 hitcount:        653
[...]

The obvious choice for the bool was already taken. I haven't found a
good name for the the flag. I guess it would make sense to refactor the
sorting code so that it doesn't really matter what kind of field it
is.

BTW, I wonder if it would possible to drop the need to always provide
the 'val' argument and just assume the 'val=hitcount' in this case.

Not for inclusion!

Not-Signed-off-by: Daniel Wagner <daniel.wagner@bmw-carit.de>
---
 kernel/trace/trace_events_hist.c | 35 +++++++++++++++++++++++++++++++----
 1 file changed, 31 insertions(+), 4 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 9a7a675..fe06707 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -89,6 +89,7 @@ enum hist_field_flags {
 struct hist_trigger_sort_key {
 	bool		use_hitcount;
 	bool		use_key;
+	bool		use_real_key;
 	bool		descending;
 	unsigned int	idx;
 };
@@ -260,7 +261,7 @@ static void destroy_hist_fields(struct hist_trigger_data *hist_data)
 	}
 }
 
-static inline struct hist_trigger_sort_key *create_default_sort_key(void)
+static inline struct hist_trigger_sort_key *create_hitcount_sort_key(void)
 {
 	struct hist_trigger_sort_key *sort_key;
 
@@ -273,6 +274,19 @@ static inline struct hist_trigger_sort_key *create_default_sort_key(void)
 	return sort_key;
 }
 
+static inline struct hist_trigger_sort_key *create_real_key_sort_key(void)
+{
+	struct hist_trigger_sort_key *sort_key;
+
+	sort_key = kzalloc(sizeof(*sort_key), GFP_KERNEL);
+	if (!sort_key)
+		return ERR_PTR(-ENOMEM);
+
+	sort_key->use_real_key = true;
+
+	return sort_key;
+}
+
 static inline struct hist_trigger_sort_key *
 create_sort_key(char *field_name, struct hist_trigger_data *hist_data)
 {
@@ -280,7 +294,10 @@ create_sort_key(char *field_name, struct hist_trigger_data *hist_data)
 	unsigned int i;
 
 	if (!strcmp(field_name, "hitcount"))
-		return create_default_sort_key();
+		return create_hitcount_sort_key();
+
+	if (!strcmp(field_name, hist_data->key->field->name))
+		return create_real_key_sort_key();
 
 	for (i = 0; i < hist_data->n_vals; i++)
 		if (!strcmp(field_name, hist_data->vals[i]->field->name))
@@ -306,7 +323,7 @@ static int create_sort_keys(struct hist_trigger_data *hist_data)
 	int ret = 0;
 
 	if (!fields_str) {
-		sort_key = create_default_sort_key();
+		sort_key = create_hitcount_sort_key();
 		if (IS_ERR(sort_key)) {
 			ret = PTR_ERR(sort_key);
 			goto out;
@@ -984,6 +1001,12 @@ static int cmp_entries(const struct hist_trigger_sort_entry **a,
 	hist_data = entry_a->hist_data;
 	sort_key = hist_data->sort_key_cur;
 
+	if (sort_key->use_real_key) {
+		val_a = *(u64 *)entry_a->key;
+		val_b = *(u64 *)entry_b->key;
+		goto out;
+	}
+
 	if (sort_key->use_key) {
 		if (memcmp((*a)->key, (*b)->key, hist_data->map->key_size))
 			ret = 1;
@@ -998,6 +1021,7 @@ static int cmp_entries(const struct hist_trigger_sort_entry **a,
 		val_b = atomic64_read(&entry_b->sums[sort_key->idx]);
 	}
 
+out:
 	if (val_a > val_b)
 		ret = 1;
 	else if (val_a < val_b)
@@ -1372,7 +1396,10 @@ static int event_hist_trigger_print(struct seq_file *m,
 		else {
 			unsigned int idx = hist_data->sort_keys[i]->idx;
 
-			hist_field_print(m, hist_data->vals[idx]);
+			if (hist_data->sort_keys[i]->use_real_key)
+				hist_field_print(m, hist_data->key);
+			else
+				hist_field_print(m, hist_data->vals[idx]);
 		}
 	}
 
-- 
2.1.0