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tracing/filter: Use a tree instead of stack for filter_match_preds()

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Currently the filter_match_preds() requires a stack to push
and pop the preds to determine if the filter matches the record or not.
This has two drawbacks:

1) It requires a stack to store state information. As this is done
   in fast paths we can't allocate the storage for this stack, and
   we can't use a global as it must be re-entrant. The stack is stored
   on the kernel stack and this greatly limits how many preds we
   may allow.

2) All conditions are calculated even when a short circuit exists.
   a || b  will always calculate a and b even though a was determined
   to be true.

Using a tree we can walk a constant structure that will save
the state as we go. The algorithm is simply:

  pred = root;
  do {
	switch (move) {
	case MOVE_DOWN:
		if (OR or AND) {
			pred = left;
			continue;
		}
		if (pred == root)
			break;
		match = pred->fn();
		pred = pred->parent;
		move = left child ? MOVE_UP_FROM_LEFT : MOVE_UP_FROM_RIGHT;
		continue;

	case MOVE_UP_FROM_LEFT:
		/* Only OR or AND can be a parent */
		if (match && OR || !match && AND) {
			/* short circuit */
			if (pred == root)
				break;
			pred = pred->parent;
			move = left child ?
				MOVE_UP_FROM_LEFT :
				MOVE_UP_FROM_RIGHT;
			continue;
		}
		pred = pred->right;
		move = MOVE_DOWN;
		continue;

	case MOVE_UP_FROM_RIGHT:
		if (pred == root)
			break;
		pred = pred->parent;
		move = left child ? MOVE_UP_FROM_LEFT : MOVE_UP_FROM_RIGHT;
		continue;
	}
	done = 1;
  } while (!done);

This way there's no strict limit to how many preds we allow
and it also will short circuit the logical operations when possible.

Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Steven Rostedt 2011-01-27 22:54:33 -05:00 • committed by Steven Rostedt
parent f76690afd0
commit 61e9dea20e
2 changed files with 194 additions and 46 deletions
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9
kernel/trace/trace.h
View file

@ -664,6 +664,7 @@ struct event_filter {
int n_preds; /* Number assigned */
int a_preds; /* allocated */
struct filter_pred *preds;
struct filter_pred *root;
char *filter_string;
};
@ -675,6 +676,9 @@ struct event_subsystem {
int nr_events;
};
#define FILTER_PRED_INVALID ((unsigned short)-1)
#define FILTER_PRED_IS_RIGHT (1 << 15)
struct filter_pred;
struct regex;
@ -704,7 +708,10 @@ struct filter_pred {
int offset;
int not;
int op;
int pop_n;
unsigned short index;
unsigned short parent;
unsigned short left;
unsigned short right;
};
extern struct list_head ftrace_common_fields;