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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 f23c4b3924 ("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: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210928093100.27124-1-lmb@cloudflare.com
This commit is contained in:
Lorenz Bauer 2021-09-28 10:30:59 +01:00 committed by Alexei Starovoitov
parent 66fe332417
commit de21d8bf77
1 changed files with 4 additions and 2 deletions
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6
net/bpf/test_run.c
View File

@ -803,7 +803,8 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
if (ret)
goto free_data;
bpf_prog_change_xdp(NULL, prog);
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
* code so the reference count of any held netdevice will be decremented
@ -824,7 +825,8 @@ int bpf_prog_test_run_xdp(struct bpf_prog *prog, const union bpf_attr *kattr,
sizeof(struct xdp_md));
out:
bpf_prog_change_xdp(prog, NULL);
if (repeat > 1)
bpf_prog_change_xdp(prog, NULL);
free_data:
kfree(data);
free_ctx: