Re: [PATCH bpf-next v3 3/5] selftests/bpf: Test a BPF CC writing sk_pacing_*

[Martin KaFai Lau <kafai@fb.com>]

On Tue, Jun 14, 2022 at 12:44:50PM +0200, Jörn-Thorben Hinz wrote:
> Test whether a TCP CC implemented in BPF is allowed to write
> sk_pacing_rate and sk_pacing_status in struct sock. This is needed when
> cong_control() is implemented and used.
> 
> Signed-off-by: Jörn-Thorben Hinz <jthinz@mailbox.tu-berlin.de>
> ---
>  .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 21 +++++++
>  .../bpf/progs/tcp_ca_write_sk_pacing.c        | 60 +++++++++++++++++++
>  2 files changed, 81 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.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 e9a9a31b2ffe..a797497e2864 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
> @@ -9,6 +9,7 @@
>  #include "bpf_cubic.skel.h"
>  #include "bpf_tcp_nogpl.skel.h"
>  #include "bpf_dctcp_release.skel.h"
> +#include "tcp_ca_write_sk_pacing.skel.h"
>  
>  #ifndef ENOTSUPP
>  #define ENOTSUPP 524
> @@ -322,6 +323,24 @@ static void test_rel_setsockopt(void)
>  	bpf_dctcp_release__destroy(rel_skel);
>  }
>  
> +static void test_write_sk_pacing(void)
> +{
> +	struct tcp_ca_write_sk_pacing *skel;
> +	struct bpf_link *link;
> +
> +	skel = tcp_ca_write_sk_pacing__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "open_and_load")) {
nit. Remove this single line '{'.

./scripts/checkpatch.pl has reported that also:
WARNING: braces {} are not necessary for single statement blocks
#43: FILE: tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c:332:
+	if (!ASSERT_OK_PTR(skel, "open_and_load")) {
+		return;
+	}


> +		return;
> +	}
> +
> +	link = bpf_map__attach_struct_ops(skel->maps.write_sk_pacing);
> +	if (ASSERT_OK_PTR(link, "attach_struct_ops")) {
Same here.

and no need to check the link before bpf_link__destroy.
bpf_link__destroy can handle error link.  Something like:

	ASSERT_OK_PTR(link, "attach_struct_ops");
	bpf_link__destroy(link);
	tcp_ca_write_sk_pacing__destroy(skel);

The earlier examples in test_cubic and test_dctcp were
written before bpf_link__destroy can handle error link.

> +		bpf_link__destroy(link);
> +	}
> +
> +	tcp_ca_write_sk_pacing__destroy(skel);
> +}
> +
>  void test_bpf_tcp_ca(void)
>  {
>  	if (test__start_subtest("dctcp"))
> @@ -334,4 +353,6 @@ void test_bpf_tcp_ca(void)
>  		test_dctcp_fallback();
>  	if (test__start_subtest("rel_setsockopt"))
>  		test_rel_setsockopt();
> +	if (test__start_subtest("write_sk_pacing"))
> +		test_write_sk_pacing();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c b/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c
> new file mode 100644
> index 000000000000..43447704cf0e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/tcp_ca_write_sk_pacing.c
> @@ -0,0 +1,60 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include "vmlinux.h"
> +
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +char _license[] SEC("license") = "GPL";
> +
> +#define USEC_PER_SEC 1000000UL
> +
> +#define min(a, b) ((a) < (b) ? (a) : (b))
> +
> +static inline struct tcp_sock *tcp_sk(const struct sock *sk)
> +{
This helper is already available in bpf_tcp_helpers.h.
Is there a reason not to use that one and redefine
it in both patch 3 and 4?  The mss_cache and srtt_us can be added
to bpf_tcp_helpers.h.  It will need another effort to move
all selftest's bpf-cc to vmlinux.h.

> +	return (struct tcp_sock *)sk;
> +}
> +
> +SEC("struct_ops/write_sk_pacing_init")
> +void BPF_PROG(write_sk_pacing_init, struct sock *sk)
> +{
> +#ifdef ENABLE_ATOMICS_TESTS
> +	__sync_bool_compare_and_swap(&sk->sk_pacing_status, SK_PACING_NONE,
> +				     SK_PACING_NEEDED);
> +#else
> +	sk->sk_pacing_status = SK_PACING_NEEDED;
> +#endif
> +}
> +
> +SEC("struct_ops/write_sk_pacing_cong_control")
> +void BPF_PROG(write_sk_pacing_cong_control, struct sock *sk,
> +	      const struct rate_sample *rs)
> +{
> +	const struct tcp_sock *tp = tcp_sk(sk);
> +	unsigned long rate =
> +		((tp->snd_cwnd * tp->mss_cache * USEC_PER_SEC) << 3) /
> +		(tp->srtt_us ?: 1U << 3);
> +	sk->sk_pacing_rate = min(rate, sk->sk_max_pacing_rate);
> +}
> +
> +SEC("struct_ops/write_sk_pacing_ssthresh")
> +__u32 BPF_PROG(write_sk_pacing_ssthresh, struct sock *sk)
> +{
> +	return tcp_sk(sk)->snd_ssthresh;
> +}
> +
> +SEC("struct_ops/write_sk_pacing_undo_cwnd")
> +__u32 BPF_PROG(write_sk_pacing_undo_cwnd, struct sock *sk)
> +{
> +	return tcp_sk(sk)->snd_cwnd;
> +}
> +
> +SEC(".struct_ops")
> +struct tcp_congestion_ops write_sk_pacing = {
> +	.init = (void *)write_sk_pacing_init,
> +	.cong_control = (void *)write_sk_pacing_cong_control,
> +	.ssthresh = (void *)write_sk_pacing_ssthresh,
> +	.undo_cwnd = (void *)write_sk_pacing_undo_cwnd,
> +	.name = "bpf_w_sk_pacing",
> +};
> -- 
> 2.30.2
>