> On Feb 22, 2022, at 8:32 PM, Yonghong Song <yhs@xxxxxx> wrote:
>
>
>
> On 2/22/22 7:13 PM, Andrii Nakryiko wrote:
>> On Tue, Feb 22, 2022 at 12:35 PM Mykola Lysenko <mykolal@xxxxxx> wrote:
>>>
>>> Thanks for the review Andrii!
>>>
>>>> On Feb 19, 2022, at 8:39 PM, Andrii Nakryiko <andrii.nakryiko@xxxxxxxxx> wrote:
>>>>
>>>> On Fri, Feb 18, 2022 at 4:30 PM Mykola Lysenko <mykolal@xxxxxx> 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@xxxxxx>
>>>>> ---
>>>>> .../testing/selftests/bpf/prog_tests/bpf_cookie.c | 2 +-
>>>>> tools/testing/selftests/bpf/prog_tests/find_vma.c | 5 ++---
>>>>> .../selftests/bpf/prog_tests/perf_branches.c | 4 ++--
>>>>> tools/testing/selftests/bpf/prog_tests/perf_link.c | 2 +-
>>>>> .../testing/selftests/bpf/prog_tests/send_signal.c | 14 ++++++++++----
>>>>> 5 files changed, 16 insertions(+), 11 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..acc41223a112 100644
>>>>> --- a/tools/testing/selftests/bpf/prog_tests/find_vma.c
>>>>> +++ b/tools/testing/selftests/bpf/prog_tests/find_vma.c
>>>>> @@ -30,7 +30,7 @@ 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;
>>>>> @@ -57,7 +57,7 @@ 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; ++i)
>>>>
>>>> 1bln seems excessive... maybe 10mln would be enough?
>>>
>>> See explanation for send_signal test case below
>>>
>>>>
>>>>> ++j;
>>>>>
>>>>> test_and_reset_skel(skel, -EBUSY /* in nmi, irq_work is busy */);
>>>>
>>>> [...]
>>>>
>>>>> diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c
>>>>> index 776916b61c40..841217bd1df6 100644
>>>>> --- a/tools/testing/selftests/bpf/prog_tests/send_signal.c
>>>>> +++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c
>>>>> @@ -4,11 +4,12 @@
>>>>> #include <sys/resource.h>
>>>>> #include "test_send_signal_kern.skel.h"
>>>>>
>>>>> -int sigusr1_received = 0;
>>>>> +int sigusr1_received;
>>>>> +volatile int volatile_variable;
>>>>
>>>> please make them static
>>>
>>> sure
>>>
>>>>
>>>>>
>>>>> static void sigusr1_handler(int signum)
>>>>> {
>>>>> - sigusr1_received++;
>>>>> + sigusr1_received = 1;
>>>>> }
>>>>>
>>>>> static void test_send_signal_common(struct perf_event_attr *attr,
>>>>> @@ -42,7 +43,9 @@ static void test_send_signal_common(struct perf_event_attr *attr,
>>>>> int old_prio;
>>>>>
>>>>> /* install signal handler and notify parent */
>>>>> + errno = 0;
>>>>> signal(SIGUSR1, sigusr1_handler);
>>>>> + ASSERT_OK(errno, "signal");
>>>>
>>>> just ASSERT_OK(signal(...), "signal");
>>>
>>> I am fine to merge signal and ASSERT lines, but will substitute with condition "signal(SIGUSR1, sigusr1_handler) != SIG_ERR”, sounds good?
>>>
>> Ah, signal is a bit special with return values. Yeah,
>> ASSERT_NEQ(signal(...), SIG_ERR, "signal") sounds good.
>>>>
>>>>>
>>>>> close(pipe_c2p[0]); /* close read */
>>>>> close(pipe_p2c[1]); /* close write */
>>>>> @@ -63,9 +66,12 @@ 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 < 1000000000; i++)
>>>>
>>>> same about 1bln
>>>
>>> With 10mln and 100 test runs I got 86 failures
>>> 100mln - 63 failures
>>> 1bln - 0 failures on 100 runs
>>>
>>> Now, there is performance concern for this test. Running
>>>
>>> time sudo ./test_progs -t send_signal/send_signal_nmi_thread
>>>
>>> With 1bln takes ~4s
>>> 100mln - 1s.
>>> Unchanged test with sleep(1); takes ~2s.
>>>
>>> On the other hand 300mln runs ~2s, and only fails 1 time per 100 runs. As 300mln does not regress performance comparing to the current “sleep(1)” implementation, I propose to go with it. What do you think?
>> I think if we need to burn multiple seconds of CPU to make the test
>> reliable, then we should either rework or disable/remove the test. In
>> CI those billions of iterations will be much slower. And even waiting
>> for 4 seconds for just one test is painful.
>> Yonghong, WDYT? Should we just drop thi test? It has caused us a bunch
>> of flakiness and maintenance burden without actually catching any
>> issues. Maybe it's better to just get rid of it?
>
> Could we try to set affinity for the child process here?
> See perf_branches.c:
>
> ...
> /* generate some branches on cpu 0 */
> CPU_ZERO(&cpu_set);
> CPU_SET(0, &cpu_set);
> err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
> if (CHECK(err, "set_affinity", "cpu #0, err %d\n", err))
> goto out_destroy;
> /* spin the loop for a while (random high number) */
> for (i = 0; i < 1000000; ++i)
> ++j;
> ...
>
> Binding the process (single thread) to a particular cpu can
> prevent other non-binding processes from migrating to this
> cpu and boost the chance for NMI triggered on this cpu.
> This could be the reason perf_branches.c (and a few other tests)
> does.
>
> In send_signal case, the cpu affinity probably should
> set to cpu 1 as cpu 0 has been pinned by previous tests for
> the main process and I didn't see it 'unpinned'
> (by setaffinity to ALL cpus).
> This is inconvenient.
>
> So the following is my suggestion:
> 1. abstract the above 'pthread_setaffinity_np to
> a helper to set affinity to a particular cpu as
> this function has been used in several cases.
> 2. create a new helper to undo setaffinity (set cpu
> mask to all available cpus) so we can pair it
> with pthread_setaffinity_np helper in prog_tests/...
> files.
> 3. clean up prog_tests/... files which have pthread_setaffinity_np.
> 4. use helpers 1/2 with loop bound 1000000 for send_signal test.
> The implementation here will be consistent with
> other NMI tests. Hopefully the test can consistent
> pass similar to other NMI tests.
>
> WDYT?
Hi Yonghong,
I have tried this approach in the send_signal test without much success unfortunately (different CPUs and configurations options). It is required though for perf_branches test, yet to understand why.
In the V2 of this patch, I used modified approach when we will stop crunching volatile variable when needed condition became true. I hope this will be an acceptable middle ground in this case.
Thanks!
>
>>>
>>>>
>>>>> + volatile_variable++;
>>>>>
>>>>> 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 */
>>>>> @@ -110,9 +116,9 @@ static void test_send_signal_common(struct perf_event_attr *attr,
>>>>> ASSERT_EQ(read(pipe_c2p[0], buf, 1), 1, "pipe_read");
>>>>>
>>>>> /* trigger the bpf send_signal */
>>>>> + skel->bss->signal_thread = signal_thread;
>>>>> skel->bss->pid = pid;
>>>>> skel->bss->sig = SIGUSR1;
>>>>> - skel->bss->signal_thread = signal_thread;
>>>>>
>>>>> /* notify child that bpf program can send_signal now */
>>>>> ASSERT_EQ(write(pipe_p2c[1], buf, 1), 1, "pipe_write");
>>>>> --
>>>>> 2.30.2
