Commit 590eee42 authored by Eduard Zingerman's avatar Eduard Zingerman Committed by Alexei Starovoitov
Browse files

bpf: do not update state->loop_entry in get_loop_entry() 

The patch 9 is simpler if less places modify loop_entry field.
The loop deleted by this patch does not affect correctness, but is a
performance optimization. However, measurements on selftests and
sched_ext programs show that this optimization is unnecessary:
- at most 2 steps are done in get_loop_entry();
- most of the time 0 or 1 steps are done in get_loop_entry().

Measured using "do-not-submit" patches from here:
https://github.com/eddyz87/bpf/tree/get-loop-entry-hungup



Signed-off-by: default avatarEduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20250215110411.3236773-8-eddyz87@gmail.com


Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
parent bb7abf30

kernel/bpf/verifier.c

+2 −11
Original line number Diff line number Diff line
@@ -1829,13 +1829,12 @@ static bool same_callsites(struct bpf_verifier_state *a, struct bpf_verifier_sta 
 *   and cur's loop entry has to be updated (case A), handle this in

 *   update_branch_counts();

 * - use st->branch > 0 as a signal that st is in the current DFS path;

 * - handle cases B and C in is_state_visited();

 * - update topmost loop entry for intermediate states in get_loop_entry().

 * - handle cases B and C in is_state_visited().

 */

static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,

						 struct bpf_verifier_state *st)

{

	struct bpf_verifier_state *topmost = st->loop_entry, *old;

	struct bpf_verifier_state *topmost = st->loop_entry;

	u32 steps = 0;









	while (topmost && topmost->loop_entry) {










@@ -1846,14 +1845,6 @@ static struct bpf_verifier_state *get_loop_entry(struct bpf_verifier_env *env,







		}









		topmost = topmost->loop_entry;









	}









	/* Update loop entries for intermediate states to avoid this









	 * traversal in future get_loop_entry() calls.









	 */









	while (st && st->loop_entry != topmost) {









		old = st->loop_entry;









		st->loop_entry = topmost;









		st = old;









	}









	return topmost;









}