Re: [PATCH bpf-next v5 8/8] selftests/bpf: Test switching TCP Congestion Control algorithms.

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

On 3/8/23 15:10, Martin KaFai Lau wrote:
> On 3/7/23 4:50 PM, Kui-Feng Lee 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);
> 
> nit. Use 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);
>> +    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");
>> +
>> +    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
> 
> Not used.
> 
>> +
>> +#define min(a, b) ((a) < (b) ? (a) : (b))
> 
> Not used.
> 
>> +
>> +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,
> 
> nit. I think it is more future proof to use '.init' to bump the ca1_cnt 
> and ca2_cnt. '.init' must be called. Just in case for some unlikely 
> stack change that may not call cong_control and then need to adjust the 
> test accordingly.

Got it!

> 
> It also needs a few negative tests like creating a link with a map 
> without BPF_F_LINK. delete_elem on BPF_F_LINK map. Replace a link with a 
> different tcp-cc-name which is not supported now, ...etc.

I have added a few more today.  Replaceing a link with a different name
is something missing. Thanks!

> 
>> +    .ssthresh = (void *)ca_update_ssthresh,
>> +    .undo_cwnd = (void *)ca_update_undo_cwnd,
>> +    .name = "tcp_ca_update",
>> +};
>