Re: [PATCH bpf-next v4 9/9] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Kui-Feng Lee <sinquersw@gmail.com>]

On 3/7/23 17:10, Andrii Nakryiko wrote:
> On Tue, Mar 7, 2023 at 3:34 PM Kui-Feng Lee <kuifeng@meta.com> wrote:
>>
>> Create a pair of sockets that utilize the congestion control algorithm
>> under a particular name. Then switch up this congestion control
>> algorithm to another implementation and check whether newly created
>> connections using the same cc name now run the new implementation.
>>
>> Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
>> ---
>>   .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
>>   .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
>>   2 files changed, 100 insertions(+)
>>   create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c
>>
>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> index e980188d4124..caaa9175ee36 100644
>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
>> @@ -8,6 +8,7 @@
>>   #include "bpf_dctcp.skel.h"
>>   #include "bpf_cubic.skel.h"
>>   #include "bpf_tcp_nogpl.skel.h"
>> +#include "tcp_ca_update.skel.h"
>>   #include "bpf_dctcp_release.skel.h"
>>   #include "tcp_ca_write_sk_pacing.skel.h"
>>   #include "tcp_ca_incompl_cong_ops.skel.h"
>> @@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
>>          libbpf_set_print(old_print_fn);
>>   }
>>
>> +static void test_update_ca(void)
>> +{
>> +       struct tcp_ca_update *skel;
>> +       struct bpf_link *link;
>> +       int saved_ca1_cnt;
>> +       int err;
>> +
>> +       skel = tcp_ca_update__open();
>> +       if (!ASSERT_OK_PTR(skel, "open"))
>> +               return;
>> +
>> +       err = tcp_ca_update__load(skel);
> 
> tcp_ca_update__open_and_load()
> 
>> +       if (!ASSERT_OK(err, "load")) {
>> +               tcp_ca_update__destroy(skel);
>> +               return;
>> +       }
>> +
>> +       link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
> 
> I think it's time to generate link holder for each struct_ops map to
> the BPF skeleton, and support auto-attach of struct_ops skeleton.
> Please do that as a follow up, once this patch set lands.

Got it.

> 
>> +       ASSERT_OK_PTR(link, "attach_struct_ops");
>> +
>> +       do_test("tcp_ca_update", NULL);
>> +       saved_ca1_cnt = skel->bss->ca1_cnt;
>> +       ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
>> +
>> +       err = bpf_link__update_map(link, skel->maps.ca_update_2);
>> +       ASSERT_OK(err, "update_struct_ops");
>> +
>> +       do_test("tcp_ca_update", NULL);
>> +       ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
>> +       ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
> 
> how do we know that struct_ops programs were triggered? what
> guarantees that? if nothing, we are just adding another flaky
> networking test

When an ack is received, cong_control of ca_update_1 and ca_update_2
will be called if they are activated.  By checking ca1_cnt & ca2_cnt, we
know which one is activated.  Here, we check if the ca1_cnt keeps the
same and ca2_cnt increase to make that ca_update_2 have replaced
ca_update_1.

> 
>> +
>> +       bpf_link__destroy(link);
>> +       tcp_ca_update__destroy(skel);
>> +}
>> +
>>   void test_bpf_tcp_ca(void)
>>   {
>>          if (test__start_subtest("dctcp"))
>> @@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
>>                  test_incompl_cong_ops();
>>          if (test__start_subtest("unsupp_cong_op"))
>>                  test_unsupp_cong_op();
>> +       if (test__start_subtest("update_ca"))
>> +               test_update_ca();
>>   }
>> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>> new file mode 100644
>> index 000000000000..36a04be95df5
>> --- /dev/null
>> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
>> @@ -0,0 +1,62 @@
>> +// SPDX-License-Identifier: GPL-2.0
>> +
>> +#include "vmlinux.h"
>> +
>> +#include <bpf/bpf_helpers.h>
>> +#include <bpf/bpf_tracing.h>
>> +
>> +char _license[] SEC("license") = "GPL";
>> +
>> +int ca1_cnt = 0;
>> +int ca2_cnt = 0;
>> +
>> +#define USEC_PER_SEC 1000000UL
>> +
>> +#define min(a, b) ((a) < (b) ? (a) : (b))
>> +
>> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
>> +{
>> +       return (struct tcp_sock *)sk;
>> +}
>> +
>> +SEC("struct_ops/ca_update_1_cong_control")
>> +void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
>> +             const struct rate_sample *rs)
>> +{
>> +       ca1_cnt++;
>> +}
>> +
>> +SEC("struct_ops/ca_update_2_cong_control")
>> +void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
>> +             const struct rate_sample *rs)
>> +{
>> +       ca2_cnt++;
>> +}
>> +
>> +SEC("struct_ops/ca_update_ssthresh")
>> +__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
>> +{
>> +       return tcp_sk(sk)->snd_ssthresh;
>> +}
>> +
>> +SEC("struct_ops/ca_update_undo_cwnd")
>> +__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
>> +{
>> +       return tcp_sk(sk)->snd_cwnd;
>> +}
>> +
>> +SEC(".struct_ops.link")
>> +struct tcp_congestion_ops ca_update_1 = {
>> +       .cong_control = (void *)ca_update_1_cong_control,
>> +       .ssthresh = (void *)ca_update_ssthresh,
>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>> +       .name = "tcp_ca_update",
>> +};
>> +
>> +SEC(".struct_ops.link")
>> +struct tcp_congestion_ops ca_update_2 = {
>> +       .cong_control = (void *)ca_update_2_cong_control,
>> +       .ssthresh = (void *)ca_update_ssthresh,
>> +       .undo_cwnd = (void *)ca_update_undo_cwnd,
>> +       .name = "tcp_ca_update",
>> +};
> 
> please add a test where you combine both .struct_ops and
> .struct_ops.link, it's an obvious potentially problematic combination
> 
> as I mentioned in previous patches, let's also have a negative test
> where bpf_link__update_map() fails

Sure

> 
>> --
>> 2.34.1
>>