Liveness analysis DFA computes a set of registers live before each
instruction. Leverage this information to skip comparison of dead
registers in func_states_equal(). This helps with convergance of
iterator processing loops, as bpf_reg_state->live marks can't be used
when loops are processed.
This has certain performance impact for selftests, here is a veristat
listing using `-f "insns_pct>5" -f "!insns<200"`
selftests:
File Program States (A) States (B) States (DIFF)
-------------------- ----------------------------- ---------- ---------- --------------
arena_htab.bpf.o arena_htab_llvm 37 35 -2 (-5.41%)
arena_htab_asm.bpf.o arena_htab_asm 37 33 -4 (-10.81%)
arena_list.bpf.o arena_list_add 37 22 -15 (-40.54%)
dynptr_success.bpf.o test_dynptr_copy 22 16 -6 (-27.27%)
dynptr_success.bpf.o test_dynptr_copy_xdp 68 58 -10 (-14.71%)
iters.bpf.o checkpoint_states_deletion 918 40 -878 (-95.64%)
iters.bpf.o clean_live_states 136 66 -70 (-51.47%)
iters.bpf.o iter_nested_deeply_iters 43 37 -6 (-13.95%)
iters.bpf.o iter_nested_iters 72 62 -10 (-13.89%)
iters.bpf.o iter_pass_iter_ptr_to_subprog 30 26 -4 (-13.33%)
iters.bpf.o iter_subprog_iters 68 59 -9 (-13.24%)
iters.bpf.o loop_state_deps2 35 32 -3 (-8.57%)
iters_css.bpf.o iter_css_for_each 32 29 -3 (-9.38%)
pyperf600_iter.bpf.o on_event 286 192 -94 (-32.87%)
Total progs: 3577
Old success: 2060
New success: 2060
States diff min: -95.64%
States diff max: 0.00%
-100 .. -90 %: 1
-55 .. -45 %: 3
-45 .. -35 %: 2
-35 .. -25 %: 5
-20 .. -10 %: 12
-10 .. 0 %: 6
sched_ext:
File Program States (A) States (B) States (DIFF)
----------------- ---------------------- ---------- ---------- ---------------
bpf.bpf.o lavd_dispatch 8950 7065 -1885 (-21.06%)
bpf.bpf.o lavd_init 516 480 -36 (-6.98%)
bpf.bpf.o layered_dispatch 662 501 -161 (-24.32%)
bpf.bpf.o layered_dump 298 237 -61 (-20.47%)
bpf.bpf.o layered_init 523 423 -100 (-19.12%)
bpf.bpf.o layered_init_task 24 22 -2 (-8.33%)
bpf.bpf.o layered_runnable 151 125 -26 (-17.22%)
bpf.bpf.o p2dq_dispatch 66 53 -13 (-19.70%)
bpf.bpf.o p2dq_init 170 142 -28 (-16.47%)
bpf.bpf.o refresh_layer_cpumasks 120 78 -42 (-35.00%)
bpf.bpf.o rustland_init 37 34 -3 (-8.11%)
bpf.bpf.o rustland_init 37 34 -3 (-8.11%)
bpf.bpf.o rusty_select_cpu 125 108 -17 (-13.60%)
scx_central.bpf.o central_dispatch 59 43 -16 (-27.12%)
scx_central.bpf.o central_init 39 28 -11 (-28.21%)
scx_nest.bpf.o nest_init 58 51 -7 (-12.07%)
scx_pair.bpf.o pair_dispatch 142 111 -31 (-21.83%)
scx_qmap.bpf.o qmap_dispatch 174 141 -33 (-18.97%)
scx_qmap.bpf.o qmap_init 768 654 -114 (-14.84%)
Total progs: 216
Old success: 186
New success: 186
States diff min: -35.00%
States diff max: 0.00%
-35 .. -25 %: 3
-25 .. -20 %: 6
-20 .. -15 %: 6
-15 .. -5 %: 7
-5 .. 0 %: 6
Signed-off-by: Eduard Zingerman <eddyz87@xxxxxxxxx>
---
kernel/bpf/verifier.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 09298e0e4b73..9685b283224a 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -18500,15 +18500,17 @@ static bool refsafe(struct bpf_verifier_state *old, struct bpf_verifier_state *c
* the current state will reach 'bpf_exit' instruction safely
*/
static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_state *old,
- struct bpf_func_state *cur, enum exact_level exact)
+ struct bpf_func_state *cur, u32 insn_idx, enum exact_level exact)
{
- int i;
+ u16 live_regs = env->insn_aux_data[insn_idx].live_regs_before;
+ u16 i;
if (old->callback_depth > cur->callback_depth)
return false;
for (i = 0; i < MAX_BPF_REG; i++)
- if (!regsafe(env, &old->regs[i], &cur->regs[i],
+ if (((1 << i) & live_regs) &&
+ !regsafe(env, &old->regs[i], &cur->regs[i],
&env->idmap_scratch, exact))
return false;
@@ -18529,6 +18531,7 @@ static bool states_equal(struct bpf_verifier_env *env,
struct bpf_verifier_state *cur,
enum exact_level exact)
{
+ u32 insn_idx;
int i;
if (old->curframe != cur->curframe)
@@ -18552,9 +18555,12 @@ static bool states_equal(struct bpf_verifier_env *env,
* and all frame states need to be equivalent
*/
for (i = 0; i <= old->curframe; i++) {
+ insn_idx = i == old->curframe
+ ? env->insn_idx
+ : old->frame[i + 1]->callsite;
if (old->frame[i]->callsite != cur->frame[i]->callsite)
return false;
- if (!func_states_equal(env, old->frame[i], cur->frame[i], exact))
+ if (!func_states_equal(env, old->frame[i], cur->frame[i], insn_idx, exact))
return false;
}
return true;
--
2.48.1
