[LTP] [PATCH] syscalls/clock_gettime: Add test to check bug during successive readings

[Viresh Kumar]

On 08-06-20, 16:51, Arnd Bergmann wrote:
> You already have a special case for gettimeofday(), so just round down
> the 'start' value to the previous microsecond when you are in that
> case.

Since this will also affect the next reading as well (as we will loose
values < 1 us), I tried to do it a bit differently.

@@ -78,6 +78,13 @@ static void run(unsigned int i)
                        tv->gettime(clks[i], tst_ts_get(&ts));
                        end = tst_ts_to_ns(ts);
 
+                       /*
+                        * gettimeofday() doesn't value less than 1 us, copy
+                        * that from start.
+                        */
+                       if (tv->gettime == my_gettimeofday && end < start)
+                               end += start % 1000;
+
                        /* Skip comparison on first traversal */
                        if (count == 10000 && !j)
                                continue;

> > +static void run(unsigned int i)
> > +{
> > +       struct tst_ts ts;
> > +       long long start, end = 0, diff;
> > +       struct test_variants *tv;
> > +       int count = 10000;
> > +       unsigned int j;
> > +
> > +       do {
> > +               for (j = 0; j < ARRAY_SIZE(variants); j++) {
> > +                       /* Refresh time in start */
> > +                       start = end;
> > +
> > +                       tv = &variants[j];
> > +                       ts.type = tv->type;
> > +
> > +                       /* Do gettimeofday() test only for CLOCK_REALTIME */
> > +                       if (tv->gettime == my_gettimeofday && clks[i] != CLOCK_REALTIME)
> > +                               continue;
> > +
> > +                       tv->gettime(clks[i], tst_ts_get(&ts));
> > +                       end = tst_ts_to_ns(ts);
> > +
> > +                       /* Skip comparison on first traversal */
> > +                       if (count == 10000 && !j)
> > +                               continue;

I am skipping diff for the first iteration..

> > +
> > +                       diff = end - start;
> 
> I think on the first iteration, 'start' is wrong here as well, and needs to
> be initialized once, as you did in the earlier versions.

And so this won't be a problem.

-- 
viresh