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

[Mykola Lysenko <mykolal@fb.com>]

> On Mar 1, 2022, at 9:23 PM, Yonghong Song <yhs@fb.com> wrote:
> 
> 
> 
> 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>

Thanks for the review!

> 
>> ---
>>  .../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.

Debugged this test a bit more, and it seems we should continue iterating when -16 is returned, as it converges to 0 eventually and test passes.

Will you be ok to add check that find_zero_ret == -1 or == -16?

> 
>> +		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.

Sounds good

> 
>>    		/* 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 */
> [...]