Re: [PATCH bpf-next] bpf: do not invoke the XDP dispatcher for PROG_RUN with single repeat

[Alexei Starovoitov]

On Tue, Sep 28, 2021 at 2:31 AM Lorenz Bauer <lmb@xxxxxxxxxxxxxx> wrote:
>
> 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 f23c4b3924d2 ("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@xxxxxxxxxxxxxx/
>
> Signed-off-by: Lorenz Bauer <lmb@xxxxxxxxxxxxxx>

Applied. Thanks