Hi Paul,
Looks like sync rcu_tasks_trace got slower or we simply didn't notice
it earlier.
In selftests/bpf try:
time ./test_progs -t trampoline_count
#101 trampoline_count:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
real 1m17.082s
user 0m0.145s
sys 0m1.369s
But with the following hack:
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 7dd523a7e32d..c417b817ec5d 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -217,7 +217,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr)
* programs finish executing.
* Wait for these two grace periods together.
*/
- synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
+// synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
I see:
time ./test_progs -t trampoline_count
#101 trampoline_count:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
real 0m1.588s
user 0m0.131s
sys 0m1.342s
It takes an extra minute to do 40 sync rcu_tasks_trace calls.
It means that every sync takes more than a second.
That feels excessive.
Doing:
- synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
+ synchronize_rcu();
is also fast:
time ./test_progs -t trampoline_count
#101 trampoline_count:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
real 0m2.089s
user 0m0.139s
sys 0m1.282s
sync rcu_tasks() is fast too:
- synchronize_rcu_mult(call_rcu_tasks, call_rcu_tasks_trace);
+ synchronize_rcu_tasks();
time ./test_progs -t trampoline_count
#101 trampoline_count:OK
Summary: 1/0 PASSED, 0 SKIPPED, 0 FAILED
real 0m2.209s
user 0m0.117s
sys 0m1.344s
so it's really something going on with sync rcu_tasks_trace.
Could you please take a look?
