Re: [PATCH v2 bpf-next] Improve BPF test stability (related to perf events and scheduling)

[Yonghong Song <yhs@fb.com>]

On 2/28/22 7:39 PM, Mykola Lysenko wrote:
> In send_signal, replace sleep with dummy cpu intensive computation
> to increase probability of child process being scheduled. Add few
> more asserts.
> 
> In find_vma, reduce sample_freq as higher values may be rejected in
> some qemu setups, remove usleep and increase length of cpu intensive
> computation.
> 
> In bpf_cookie, perf_link and perf_branches, reduce sample_freq as
> higher values may be rejected in some qemu setups
> 
> Signed-off-by: Mykola Lysenko <mykolal@fb.com>

LGTM with a few nits below.

Acked-by: Yonghong Song <yhs@fb.com>

> ---
>   .../selftests/bpf/prog_tests/bpf_cookie.c       |  2 +-
>   .../testing/selftests/bpf/prog_tests/find_vma.c | 13 ++++++++++---
>   .../selftests/bpf/prog_tests/perf_branches.c    |  4 ++--
>   .../selftests/bpf/prog_tests/perf_link.c        |  2 +-
>   .../selftests/bpf/prog_tests/send_signal.c      | 17 ++++++++++-------
>   .../selftests/bpf/progs/test_send_signal_kern.c |  2 +-
>   6 files changed, 25 insertions(+), 15 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
> index cd10df6cd0fc..0612e79a9281 100644
> --- a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
> @@ -199,7 +199,7 @@ static void pe_subtest(struct test_bpf_cookie *skel)
>   	attr.type = PERF_TYPE_SOFTWARE;
>   	attr.config = PERF_COUNT_SW_CPU_CLOCK;
>   	attr.freq = 1;
> -	attr.sample_freq = 4000;
> +	attr.sample_freq = 1000;
>   	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
>   	if (!ASSERT_GE(pfd, 0, "perf_fd"))
>   		goto cleanup;
> diff --git a/tools/testing/selftests/bpf/prog_tests/find_vma.c b/tools/testing/selftests/bpf/prog_tests/find_vma.c
> index b74b3c0c555a..a0b68381cd79 100644
> --- a/tools/testing/selftests/bpf/prog_tests/find_vma.c
> +++ b/tools/testing/selftests/bpf/prog_tests/find_vma.c
> @@ -30,12 +30,20 @@ static int open_pe(void)
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_CPU_CYCLES;
>   	attr.freq = 1;
> -	attr.sample_freq = 4000;
> +	attr.sample_freq = 1000;
>   	pfd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, PERF_FLAG_FD_CLOEXEC);
>   
>   	return pfd >= 0 ? pfd : -errno;
>   }
>   
> +static bool find_vma_pe_condition(struct find_vma *skel)
> +{
> +	return skel->bss->found_vm_exec != 1 ||

In test_and_reset_skel(), we have following codes for reset/default values:
         skel->bss->found_vm_exec = 0;
         skel->data->find_addr_ret = -1;
         skel->data->find_zero_ret = -1;
         skel->bss->d_iname[0] = 0;

I think we should stick to them, so it would be good
to change
	skel->bss->found_vm_exec != 1
to
	skel->bss->found_vm_exec == 0

> +		skel->data->find_addr_ret == -1 ||
> +		skel->data->find_zero_ret != 0 ||

Change
	skel->data->find_zero_ret != 0
to
	skel->data->find_zero_ret == -1

The bpf program may set skel->data->find_zero_ret to
-ENOENT (-2)  or -EBUSY (-16) in which case we should
stop the iteration.

> +		skel->bss->d_iname[0] == 0;
> +}
> +
>   static void test_find_vma_pe(struct find_vma *skel)
>   {
>   	struct bpf_link *link = NULL;
> @@ -57,7 +65,7 @@ static void test_find_vma_pe(struct find_vma *skel)
>   	if (!ASSERT_OK_PTR(link, "attach_perf_event"))
>   		goto cleanup;
>   
> -	for (i = 0; i < 1000000; ++i)
> +	for (i = 0; i < 1000000000 && find_vma_pe_condition(skel); ++i)
>   		++j;
>   
>   	test_and_reset_skel(skel, -EBUSY /* in nmi, irq_work is busy */);
> @@ -108,7 +116,6 @@ void serial_test_find_vma(void)
>   	skel->bss->addr = (__u64)(uintptr_t)test_find_vma_pe;
>   
>   	test_find_vma_pe(skel);
> -	usleep(100000); /* allow the irq_work to finish */
>   	test_find_vma_kprobe(skel);
>   
>   	find_vma__destroy(skel);
> diff --git a/tools/testing/selftests/bpf/prog_tests/perf_branches.c b/tools/testing/selftests/bpf/prog_tests/perf_branches.c
> index 12c4f45cee1a..bc24f83339d6 100644
> --- a/tools/testing/selftests/bpf/prog_tests/perf_branches.c
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_branches.c
> @@ -110,7 +110,7 @@ static void test_perf_branches_hw(void)
>   	attr.type = PERF_TYPE_HARDWARE;
>   	attr.config = PERF_COUNT_HW_CPU_CYCLES;
>   	attr.freq = 1;
> -	attr.sample_freq = 4000;
> +	attr.sample_freq = 1000;
>   	attr.sample_type = PERF_SAMPLE_BRANCH_STACK;
>   	attr.branch_sample_type = PERF_SAMPLE_BRANCH_USER | PERF_SAMPLE_BRANCH_ANY;
>   	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
> @@ -151,7 +151,7 @@ static void test_perf_branches_no_hw(void)
>   	attr.type = PERF_TYPE_SOFTWARE;
>   	attr.config = PERF_COUNT_SW_CPU_CLOCK;
>   	attr.freq = 1;
> -	attr.sample_freq = 4000;
> +	attr.sample_freq = 1000;
>   	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
>   	if (CHECK(pfd < 0, "perf_event_open", "err %d\n", pfd))
>   		return;
> diff --git a/tools/testing/selftests/bpf/prog_tests/perf_link.c b/tools/testing/selftests/bpf/prog_tests/perf_link.c
> index ede07344f264..224eba6fef2e 100644
> --- a/tools/testing/selftests/bpf/prog_tests/perf_link.c
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_link.c
> @@ -39,7 +39,7 @@ void serial_test_perf_link(void)
>   	attr.type = PERF_TYPE_SOFTWARE;
>   	attr.config = PERF_COUNT_SW_CPU_CLOCK;
>   	attr.freq = 1;
> -	attr.sample_freq = 4000;
> +	attr.sample_freq = 1000;
>   	pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
>   	if (!ASSERT_GE(pfd, 0, "perf_fd"))
>   		goto cleanup;
> diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c
> index 776916b61c40..b1b574c7016a 100644
> --- a/tools/testing/selftests/bpf/prog_tests/send_signal.c
> +++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c
> @@ -4,11 +4,11 @@
>   #include <sys/resource.h>
>   #include "test_send_signal_kern.skel.h"
>   
> -int sigusr1_received = 0;
> +static int sigusr1_received;
>   
>   static void sigusr1_handler(int signum)
>   {
> -	sigusr1_received++;
> +	sigusr1_received = 1;
>   }
>   
>   static void test_send_signal_common(struct perf_event_attr *attr,
> @@ -40,9 +40,10 @@ static void test_send_signal_common(struct perf_event_attr *attr,
>   
>   	if (pid == 0) {
>   		int old_prio;
> +		volatile int volatile_variable = 0;

I think it is okay to use variable 'j' to be consistent with other
similar codes in selftests.

>   
>   		/* install signal handler and notify parent */
> -		signal(SIGUSR1, sigusr1_handler);
> +		ASSERT_NEQ(signal(SIGUSR1, sigusr1_handler), SIG_ERR, "signal");
>   
>   		close(pipe_c2p[0]); /* close read */
>   		close(pipe_p2c[1]); /* close write */
> @@ -63,9 +64,11 @@ static void test_send_signal_common(struct perf_event_attr *attr,
>   		ASSERT_EQ(read(pipe_p2c[0], buf, 1), 1, "pipe_read");
>   
>   		/* wait a little for signal handler */
> -		sleep(1);
> +		for (int i = 0; i < 100000000 && !sigusr1_received; i++)
> +			volatile_variable /= i + 1;
>   
>   		buf[0] = sigusr1_received ? '2' : '0';
> +		ASSERT_EQ(sigusr1_received, 1, "sigusr1_received");
>   		ASSERT_EQ(write(pipe_c2p[1], buf, 1), 1, "pipe_write");
>   
>   		/* wait for parent notification and exit */
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