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Subject[PATCH 10/14] tracing/filter: Optimize filter by folding the tree
From: Steven Rostedt <srostedt@redhat.com>

There are many cases that a filter will contain multiple ORs or
ANDs together near the leafs. Walking up and down the tree to get
to the next compare can be a waste.

If there are several ORs or ANDs together, fold them into a single
pred and allocate an array of the conditions that they check.
This will speed up the filter by linearly walking an array
and can still break out if a short circuit condition is met.

Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
kernel/trace/trace.h | 12 ++-
kernel/trace/trace_events_filter.c | 233 ++++++++++++++++++++++++++++++++++--
2 files changed, 235 insertions(+), 10 deletions(-)
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index bba34a7..d754330 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -678,6 +678,7 @@ struct event_subsystem {

#define FILTER_PRED_INVALID ((unsigned short)-1)
#define FILTER_PRED_IS_RIGHT (1 << 15)
+#define FILTER_PRED_FOLD (1 << 15)

struct filter_pred;
struct regex;
@@ -704,7 +705,16 @@ struct filter_pred {
filter_pred_fn_t fn;
u64 val;
struct regex regex;
- char *field_name;
+ /*
+ * Leaf nodes use field_name, ops is used by AND and OR
+ * nodes. The field_name is always freed when freeing a pred.
+ * We can overload field_name for ops and have it freed
+ * as well.
+ */
+ union {
+ char *field_name;
+ unsigned short *ops;
+ };
int offset;
int not;
int op;
diff --git a/kernel/trace/trace_events_filter.c b/kernel/trace/trace_events_filter.c
index 91c9cdc..2403ce5 100644
--- a/kernel/trace/trace_events_filter.c
+++ b/kernel/trace/trace_events_filter.c
@@ -381,6 +381,42 @@ get_pred_parent(struct filter_pred *pred, struct filter_pred *preds,
return pred;
}

+/*
+ * A series of AND or ORs where found together. Instead of
+ * climbing up and down the tree branches, an array of the
+ * ops were made in order of checks. We can just move across
+ * the array and short circuit if needed.
+ */
+static int process_ops(struct filter_pred *preds,
+ struct filter_pred *op, void *rec)
+{
+ struct filter_pred *pred;
+ int type;
+ int match;
+ int i;
+
+ /*
+ * Micro-optimization: We set type to true if op
+ * is an OR and false otherwise (AND). Then we
+ * just need to test if the match is equal to
+ * the type, and if it is, we can short circuit the
+ * rest of the checks:
+ *
+ * if ((match && op->op == OP_OR) ||
+ * (!match && op->op == OP_AND))
+ * return match;
+ */
+ type = op->op == OP_OR;
+
+ for (i = 0; i < op->val; i++) {
+ pred = &preds[op->ops[i]];
+ match = pred->fn(pred, rec);
+ if (!!match == type)
+ return match;
+ }
+ return match;
+}
+
/* return 1 if event matches, 0 otherwise (discard) */
int filter_match_preds(struct event_filter *filter, void *rec)
{
@@ -414,11 +450,16 @@ int filter_match_preds(struct event_filter *filter, void *rec)
case MOVE_DOWN:
/* only AND and OR have children */
if (pred->left != FILTER_PRED_INVALID) {
- /* keep going to leaf node */
- pred = &preds[pred->left];
- continue;
- }
- match = pred->fn(pred, rec);
+ /* If ops is set, then it was folded. */
+ if (!pred->ops) {
+ /* keep going to down the left side */
+ pred = &preds[pred->left];
+ continue;
+ }
+ /* We can treat folded ops as a leaf node */
+ match = process_ops(preds, pred, rec);
+ } else
+ match = pred->fn(pred, rec);
/* If this pred is the only pred */
if (pred == root)
break;
@@ -659,17 +700,34 @@ static int filter_set_pred(struct event_filter *filter,
left = __pop_pred_stack(stack);
if (!left || !right)
return -EINVAL;
- dest->left = left->index;
- dest->right = right->index;
- left->parent = dest->index;
+ /*
+ * If both children can be folded
+ * and they are the same op as this op or a leaf,
+ * then this op can be folded.
+ */
+ if (left->index & FILTER_PRED_FOLD &&
+ (left->op == dest->op ||
+ left->left == FILTER_PRED_INVALID) &&
+ right->index & FILTER_PRED_FOLD &&
+ (right->op == dest->op ||
+ right->left == FILTER_PRED_INVALID))
+ dest->index |= FILTER_PRED_FOLD;
+
+ dest->left = left->index & ~FILTER_PRED_FOLD;
+ dest->right = right->index & ~FILTER_PRED_FOLD;
+ left->parent = dest->index & ~FILTER_PRED_FOLD;
right->parent = dest->index | FILTER_PRED_IS_RIGHT;
- } else
+ } else {
/*
* Make dest->left invalid to be used as a quick
* way to know this is a leaf node.
*/
dest->left = FILTER_PRED_INVALID;

+ /* All leafs allow folding the parent ops. */
+ dest->index |= FILTER_PRED_FOLD;
+ }
+
return __push_pred_stack(stack, dest);
}

@@ -1420,6 +1478,158 @@ static int check_pred_tree(struct event_filter *filter,
return 0;
}

+static int count_leafs(struct filter_pred *preds, struct filter_pred *root)
+{
+ struct filter_pred *pred;
+ enum move_type move = MOVE_DOWN;
+ int count = 0;
+ int done = 0;
+
+ pred = root;
+
+ do {
+ switch (move) {
+ case MOVE_DOWN:
+ if (pred->left != FILTER_PRED_INVALID) {
+ pred = &preds[pred->left];
+ continue;
+ }
+ /* A leaf at the root is just a leaf in the tree */
+ if (pred == root)
+ return 1;
+ count++;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ case MOVE_UP_FROM_LEFT:
+ pred = &preds[pred->right];
+ move = MOVE_DOWN;
+ continue;
+ case MOVE_UP_FROM_RIGHT:
+ if (pred == root)
+ break;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ }
+ done = 1;
+ } while (!done);
+
+ return count;
+}
+
+static int fold_pred(struct filter_pred *preds, struct filter_pred *root)
+{
+ struct filter_pred *pred;
+ enum move_type move = MOVE_DOWN;
+ int count = 0;
+ int children;
+ int done = 0;
+
+ /* No need to keep the fold flag */
+ root->index &= ~FILTER_PRED_FOLD;
+
+ /* If the root is a leaf then do nothing */
+ if (root->left == FILTER_PRED_INVALID)
+ return 0;
+
+ /* count the children */
+ children = count_leafs(preds, &preds[root->left]);
+ children += count_leafs(preds, &preds[root->right]);
+
+ root->ops = kzalloc(sizeof(*root->ops) * children, GFP_KERNEL);
+ if (!root->ops)
+ return -ENOMEM;
+
+ root->val = children;
+
+ pred = root;
+ do {
+ switch (move) {
+ case MOVE_DOWN:
+ if (pred->left != FILTER_PRED_INVALID) {
+ pred = &preds[pred->left];
+ continue;
+ }
+ if (WARN_ON(count == children))
+ return -EINVAL;
+ pred->index &= ~FILTER_PRED_FOLD;
+ root->ops[count++] = pred->index;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ case MOVE_UP_FROM_LEFT:
+ pred = &preds[pred->right];
+ move = MOVE_DOWN;
+ continue;
+ case MOVE_UP_FROM_RIGHT:
+ if (pred == root)
+ break;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ }
+ done = 1;
+ } while (!done);
+
+ return 0;
+}
+
+/*
+ * To optimize the processing of the ops, if we have several "ors" or
+ * "ands" together, we can put them in an array and process them all
+ * together speeding up the filter logic.
+ */
+static int fold_pred_tree(struct event_filter *filter,
+ struct filter_pred *root)
+{
+ struct filter_pred *preds;
+ struct filter_pred *pred;
+ enum move_type move = MOVE_DOWN;
+ int done = 0;
+ int err;
+
+ preds = filter->preds;
+ if (!preds)
+ return -EINVAL;
+ pred = root;
+
+ do {
+ switch (move) {
+ case MOVE_DOWN:
+ if (pred->index & FILTER_PRED_FOLD) {
+ err = fold_pred(preds, pred);
+ if (err)
+ return err;
+ /* Folded nodes are like leafs */
+ } else if (pred->left != FILTER_PRED_INVALID) {
+ pred = &preds[pred->left];
+ continue;
+ }
+
+ /* A leaf at the root is just a leaf in the tree */
+ if (pred == root)
+ break;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ case MOVE_UP_FROM_LEFT:
+ pred = &preds[pred->right];
+ move = MOVE_DOWN;
+ continue;
+ case MOVE_UP_FROM_RIGHT:
+ if (pred == root)
+ break;
+ pred = get_pred_parent(pred, preds,
+ pred->parent, &move);
+ continue;
+ }
+ done = 1;
+ } while (!done);
+
+ return 0;
+}
+
static int replace_preds(struct ftrace_event_call *call,
struct event_filter *filter,
struct filter_parse_state *ps,
@@ -1517,6 +1727,11 @@ add_pred:
if (err)
goto fail;

+ /* Optimize the tree */
+ err = fold_pred_tree(filter, root);
+ if (err)
+ goto fail;
+
/* We don't set root until we know it works */
barrier();
filter->root = root;
--
1.7.2.3



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