[PATCH] tst: Provide test for select

[Adhemerval Zanella]

On 24/03/2021 16:17, H.J. Lu wrote:
> On Mon, Mar 22, 2021 at 4:33 AM Lukasz Majewski <lukma@denx.de> wrote:
>>
>> Dear Community,
>>
>>> This change adds new test to assess select()'s timeout related
>>> functionality (the rdfs set provides valid fd - stderr - but during
>>> normal program operation there is no data to be read, so one just
>>> waits for timeout).
>>>
>>> To be more specific - two use cases are checked:
>>> - if select() times out immediately when passed struct timeval has
>>>   zero values of tv_usec and tv_sec.
>>> - if select() times out after timeout specified in passed argument
>>
>> Do you have any comments regarding this patch?
>>
> 
> This test failed on machines with more than 40 cores:
> 
> tst-select.c:54: 1616610088.851713938s not after 1616610089.851712804s
> (difference 0.999998866s)
> error: 1 test failures
> 
> I was doing 3 "makec -j28 check" in parallel.

I think the nanosecond precision of time accounting is triggering the
failure, since select only support timeval (the error indicates that
the nanosecond precision is what is triggering it).  

Maybe if we ignore the nanosecond precision:

diff --git a/misc/tst-select.c b/misc/tst-select.c
index 7c310256c5..4b1791ac8a 100644
--- a/misc/tst-select.c
+++ b/misc/tst-select.c
@@ -45,6 +45,8 @@ test_select_timeout (bool zero_tmo)
   to.tv_sec = timeout;
   ts = xclock_now (CLOCK_REALTIME);
   ts = timespec_add (ts, (struct timespec) { timeout, 0 });
+  /* Ignore nanosecond precision since select only support microsecond.  */
+  ts.tv_nsec = (ts.tv_nsec * 1000) / 1000;

   /* Wait for timeout.  */
   int ret = select (fds + 1, &rfds, NULL, NULL, &to);