With large verifier speed improvement brought by the previous patch mark_reg_read() becomes the hottest function during verification. On a typical program it consumes 40% of cpu. mark_reg_read() walks parentage chain of registers to mark parents as LIVE_READ. Once the register is marked there is no need to remark it again in the future. Hence stop walking the chain once first LIVE_READ is seen. This optimization drops mark_reg_read() time from 40% of cpu to <1% and overall 2x improvement of verification speed. For some programs the longest_mark_read_walk counter improves from ~500 to ~5 Signed-off-by: Alexei Starovoitov <ast@xxxxxxxxxx> --- kernel/bpf/verifier.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index b18512ac205e..6dfd148b58f6 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1151,6 +1151,15 @@ static int mark_reg_read(struct bpf_verifier_env *env, parent->var_off.value, parent->off); return -EFAULT; } + if (parent->live & REG_LIVE_READ) + /* The parentage chain never changes and + * this parent was already marked as LIVE_READ. + * There is no need to keep walking the chain again and + * keep re-marking all parents as LIVE_READ. + * This case happens when the same register is read + * multiple times without writes into it in-between. + */ + break; /* ... then we depend on parent's value */ parent->live |= REG_LIVE_READ; state = parent; -- 2.20.0
