netdev - Re: [PATCH bpf-next] selftests/bpf: fix usleep() implementation

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Date:   Thu, 12 Mar 2020 23:45:21 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andriin@...com>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...com,
        daniel@...earbox.net, andrii.nakryiko@...il.com, kernel-team@...com
Subject: Re: [PATCH bpf-next] selftests/bpf: fix usleep() implementation

On Thu, Mar 12, 2020 at 11:18:37PM -0700, Andrii Nakryiko wrote:
> nanosleep syscall expects pointer to struct timespec, not nanoseconds
> directly. Current implementation fulfills its purpose of invoking nanosleep
> syscall, but doesn't really provide sleeping capabilities, which can cause
> flakiness for tests relying on usleep() to wait for something.
> 
> Fixes: ec12a57b822c ("selftests/bpf: Guarantee that useep() calls nanosleep() syscall")
> Signed-off-by: Andrii Nakryiko <andriin@...com>
> ---
>  tools/testing/selftests/bpf/test_progs.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index 2b0bc1171c9c..b6201dd82edf 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -35,7 +35,16 @@ struct prog_test_def {
>   */
>  int usleep(useconds_t usec)
>  {
> -	return syscall(__NR_nanosleep, usec * 1000UL);
> +	struct timespec ts;
> +
> +	if (usec > 999999) {
> +		ts.tv_sec = usec / 1000000;
> +		ts.tv_nsec = usec % 1000000;
> +	} else {
> +		ts.tv_sec = 0;
> +		ts.tv_nsec = usec;
> +	}
> +	return nanosleep(&ts, NULL);
>  }

Is this a copy-paste from somewhere?
Above 'if' looks like premature optimization.
I applied it anyway, since it fixes flakiness in test_progs -n 24.
Now pin*tp* tests are stable.

But the other one is still flaky:
server_thread:FAIL:237
Failed to accept client: Resource temporarily unavailable
#64 tcp_rtt:FAIL
Note that if I run the test alone (test_progs -n 64) it is stable.
It fails only when run as part of bigger test_progs.
test_progs -n 30-64 sporadically fails (most of the time)
test_progs -n 40-64 consistently passes
Haven't bisected further.