Commit 25af32da authored Apr 01, 2019 by Alexei Starovoitov Committed by Daniel Borkmann Apr 04, 2019

bpf: improve verification speed by not remarking live_read

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@kernel.org>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Edward Cree <ecree@solarflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

parent 9f4686c4

kernel/bpf/verifier.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -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;

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