Commit de21d8bf authored by Lorenz Bauer's avatar Lorenz Bauer Committed by Alexei Starovoitov
Browse files

bpf: Do not invoke the XDP dispatcher for PROG_RUN with single repeat 

We have a unit test that invokes an XDP program with 1m different
inputs, aka 1m BPF_PROG_RUN syscalls. We run this test concurrently
with slight variations in how we generated the input.

Since commit f23c4b39 ("bpf: Start using the BPF dispatcher in BPF_TEST_RUN")
the unit test has slowed down significantly. Digging deeper reveals that
the concurrent tests are serialised in the kernel on the XDP dispatcher.
This is a global resource that is protected by a mutex, on which we contend.

Fix this by not calling into the XDP dispatcher if we only want to perform
a single run of the BPF program.

See: https://lore.kernel.org/bpf/CACAyw9_y4QumOW35qpgTbLsJ532uGq-kVW-VESJzGyiZkypnvw@mail.gmail.com/



Signed-off-by: default avatarLorenz Bauer <lmb@cloudflare.com>
Signed-off-by: default avatarAlexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210928093100.27124-1-lmb@cloudflare.com
parent 66fe3324

net/bpf/test_run.c

+4 −2
Original line number Diff line number Diff line
@@ -803,6 +803,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, 
	if (ret)

		goto free_data;



	if (repeat > 1)

		bpf_prog_change_xdp(NULL, prog);

	ret = bpf_test_run(prog, &xdp, repeat, &retval, &duration, true);

	/* We convert the xdp_buff back to an xdp_md before checking the return
@@ -824,6 +825,7 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr, 
				     sizeof(struct xdp_md));



out:

	if (repeat > 1)

		bpf_prog_change_xdp(prog, NULL);

free_data:

	kfree(data);