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From:   Alexei Starovoitov <alexei.starovoitov@gmail.com>
Date:   Wed, 29 Sep 2021 14:17:01 -0700
Message-ID: <CAADnVQ+UJ5bhRNdnHM62_XFzMp3q1-Njh80ZNvs=4=PH1jAmpw@mail.gmail.com>
Subject: Re: [PATCH bpf-next] bpf: do not invoke the XDP dispatcher for
 PROG_RUN with single repeat
To:     Lorenz Bauer <lmb@cloudflare.com>
Cc:     =?UTF-8?B?QmrDtnJuIFTDtnBlbA==?= <bjorn@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        kernel-team <kernel-team@cloudflare.com>,
        Network Development <netdev@vger.kernel.org>,
        bpf <bpf@vger.kernel.org>, LKML <linux-kernel@vger.kernel.org>
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On Tue, Sep 28, 2021 at 2:31 AM Lorenz Bauer <lmb@cloudflare.com> 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@mail.gmail.com/
>
> Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>

Applied. Thanks