[PATCH v8] Fix time/tst-cpuclock1 intermitent failures

["Lucas A. M. Magalhaes via Libc-alpha" <libc-alpha@sourceware.org>]

This test fails intermittently in systems with heavy load as
CLOCK_PROCESS_CPUTIME_ID is subject to scheduler pressure.  Thus the
test boundaries were relaxed to keep it from failing on such systems.

A refactor of the spent time checking was made with some support
functions.  With the advantage to representing time jitter in percent
of the target.

The values used by the test boundaries are all empirical.

---

Hi Carlos,
Thanks for the work and patience on this reviews.

changes on V8:
	Add support_timespec_ns
	Add more tests

changes on V7:
	- change expecting boundaries
	- add comments

changes on V6:
	- add overflow handling
	- change variables names

changes on V5:
	- add tests for support_timespec_check_in_range
	- fix support_timespec_normalize
	- add comments
	- fix style

changes on V4:
	- move functions to support/timespec.c
	- simplify functions

changes on V3:
	- refactor support functions
	- use existing timespec-sub function

changes on V2:
	- Add support functions
---
 support/Makefile       |   1 +
 support/timespec.c     |  59 ++++++++++
 support/timespec.h     |   8 ++
 support/tst-timespec.c | 241 +++++++++++++++++++++++++++++++++++++++++
 time/tst-cpuclock1.c   |  48 +++-----
 5 files changed, 327 insertions(+), 30 deletions(-)
 create mode 100644 support/tst-timespec.c

diff --git a/support/Makefile b/support/Makefile
index 6e38b87ebe..cacaac96a5 100644
--- a/support/Makefile
+++ b/support/Makefile
@@ -233,6 +233,7 @@ tests = \
   tst-test_compare \
   tst-test_compare_blob \
   tst-test_compare_string \
+  tst-timespec \
   tst-xreadlink \
   tst-xsigstack \
 
diff --git a/support/timespec.c b/support/timespec.c
index ea6b947546..156a409733 100644
--- a/support/timespec.c
+++ b/support/timespec.c
@@ -19,6 +19,8 @@
 #include <support/timespec.h>
 #include <stdio.h>
 #include <stdint.h>
+#include <assert.h>
+#include <intprops.h>
 
 void
 test_timespec_before_impl (const char *file, int line,
@@ -57,3 +59,60 @@ test_timespec_equal_or_after_impl (const char *file, int line,
 	    (intmax_t) diff.tv_sec, (intmax_t) diff.tv_nsec);
   }
 }
+
+/* Convert TIME to nanoseconds stored in shrinked.  */
+long
+support_timespec_ns (struct timespec time)
+{
+  long time_ns;
+  if (INT_MULTIPLY_WRAPV(time.tv_sec, TIMESPEC_HZ, &time_ns))
+   {
+      time_ns = (time.tv_sec < 0) ? TYPE_MINIMUM(long): TYPE_MAXIMUM(long);
+   }
+  if (INT_ADD_WRAPV(time_ns, time.tv_nsec, &time_ns))
+   {
+      time_ns = (time.tv_nsec < 0) ? TYPE_MINIMUM(long): TYPE_MAXIMUM(long);
+   }
+  return time_ns;
+}
+
+/* Returns t normalized timespec with .tv_nsec < TIMESPEC_HZ
+   and the overflows added to .tv_sec. It assumes times are
+   positive.  */
+struct timespec
+support_timespec_normalize (struct timespec time)
+{
+  struct timespec norm;
+  if (INT_ADD_WRAPV (time.tv_sec, (time.tv_nsec / TIMESPEC_HZ), &norm.tv_sec))
+   {
+     norm.tv_sec = (time.tv_nsec < 0) ? TYPE_MINIMUM (time_t):TYPE_MAXIMUM (time_t);
+   }
+  norm.tv_nsec = time.tv_nsec % TIMESPEC_HZ;
+  return norm;
+}
+
+/* Returns TRUE if the observed time is within the given percentage bounds of
+the expected time, and FALSE otherwise.
+For example the call
+
+support_timespec_check_in_range(expected, observed, .5, 1.2);
+
+will check if
+
+.5 <= observed/expected <= 1.2
+
+In other words it will check if observed time is within 50% to 120% of
+the expected time.  */
+int
+support_timespec_check_in_range (struct timespec expected, struct timespec observed,
+			      double lower_bound, double upper_bound)
+{
+  assert (upper_bound >= lower_bound);
+  long expected_norm, observed_norm;
+  expected_norm = support_timespec_ns (expected);
+  /* Don't divide by zero  */
+  assert(expected_norm != 0);
+  observed_norm = support_timespec_ns (observed);
+  double ratio = (double)observed_norm / expected_norm;
+  return (lower_bound <= ratio && ratio <= upper_bound);
+}
diff --git a/support/timespec.h b/support/timespec.h
index c5852dfe75..fd5466745d 100644
--- a/support/timespec.h
+++ b/support/timespec.h
@@ -48,6 +48,14 @@ void test_timespec_equal_or_after_impl (const char *file, int line,
                                         const struct timespec left,
                                         const struct timespec right);
 
+long support_timespec_ns (struct timespec time);
+
+struct timespec support_timespec_normalize (struct timespec time);
+
+int support_timespec_check_in_range (struct timespec expected, struct timespec observed,
+				  double lower_bound, double upper_bound);
+
+
 /* Check that the timespec on the left represents a time before the
    time on the right. */
 #define TEST_TIMESPEC_BEFORE(left, right)                               \
diff --git a/support/tst-timespec.c b/support/tst-timespec.c
new file mode 100644
index 0000000000..e9f21e6e35
--- /dev/null
+++ b/support/tst-timespec.c
@@ -0,0 +1,241 @@
+/* Test for support_timespec_check_in_range function.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <support/timespec.h>
+#include <support/check.h>
+#include <limits.h>
+
+struct timespec_ns_test_case
+{
+  struct timespec time;
+  long time_ns;
+};
+
+struct timespec_norm_test_case
+{
+  struct timespec time;
+  struct timespec norm;
+};
+
+struct timespec_test_case
+{
+  struct timespec expected;
+  struct timespec observed;
+  double upper_bound;
+  double lower_bound;
+  int result;
+};
+
+/* Test cases for timespec_ns */
+struct timespec_ns_test_case ns_cases[] = {
+  {.time = {.tv_sec = 0, .tv_nsec = 0},
+   .time_ns = 0,
+  },
+  {.time = {.tv_sec = 0, .tv_nsec = 1},
+   .time_ns = 1,
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = 0},
+   .time_ns = 1000000000,
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = 1},
+   .time_ns = 1000000001,
+  },
+  {.time = {.tv_sec = 0, .tv_nsec = -1},
+   .time_ns = -1,
+  },
+  {.time = {.tv_sec = -1, .tv_nsec = 0},
+   .time_ns = -1000000000,
+  },
+  {.time = {.tv_sec = -1, .tv_nsec = -1},
+   .time_ns = -1000000001,
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = -1},
+   .time_ns = 999999999,
+  },
+  {.time = {.tv_sec = -1, .tv_nsec = 1},
+   .time_ns = -999999999,
+  },
+  {.time = {.tv_sec = LONG_MAX, .tv_nsec = 1},
+   .time_ns = LONG_MAX,
+  },
+  {.time = {.tv_sec = LONG_MIN, .tv_nsec = -1},
+   .time_ns = LONG_MIN,
+  }
+};
+
+/* Test cases for timespec_norm */
+struct timespec_norm_test_case norm_cases[] = {
+  {.time = {.tv_sec = 0, .tv_nsec = 0},
+   .norm = {.tv_sec = 0, .tv_nsec = 0}
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = 0},
+   .norm = {.tv_sec = 1, .tv_nsec = 0}
+  },
+  {.time = {.tv_sec = 0, .tv_nsec = 1},
+   .norm = {.tv_sec = 0, .tv_nsec = 1}
+  },
+  {.time = {.tv_sec = 0, .tv_nsec = 10000000000},
+   .norm = {.tv_sec = 1, .tv_nsec = 0}
+  },
+  {.time = {.tv_sec = 0, .tv_nsec = 10000000001},
+   .norm = {.tv_sec = 1, .tv_nsec =1}
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = 10000000000},
+   .norm = {.tv_sec = 2, .tv_nsec = 0}
+  },
+  {.time = {.tv_sec = 1, .tv_nsec = 10000000001},
+   .norm = {.tv_sec = 1, .tv_nsec = 1}
+  },
+  {.time = {.tv_sec = LONG_MAX, .tv_nsec = 1000000000},
+   .norm = {.tv_sec = LONG_MAX, .tv_nsec = 0},
+  }
+};
+
+/* Test cases for timespec_check_in_range  */
+struct timespec_test_case check_cases[] = {
+  // 0 - In range
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 1, .tv_nsec = 0},
+   .upper_bound = 1, .lower_bound = 1, .result = 1,
+  },
+  // 1 - Out of range
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 2, .tv_nsec = 0},
+   .upper_bound = 1, .lower_bound = 1, .result = 0,
+  },
+  // 2 - Upper Bound
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 2, .tv_nsec = 0},
+   .upper_bound = 2, .lower_bound = 1, .result = 1,
+  },
+  // 3 - Lower Bound
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 0, .tv_nsec = 0},
+   .upper_bound = 1, .lower_bound = 0, .result = 1,
+  },
+  // 4 - Out of range by nanosecs
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 1, .tv_nsec = 500},
+   .upper_bound = 1, .lower_bound = 1, .result = 0,
+  },
+  // 5 - In range by nanosecs
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 1, .tv_nsec = 50000},
+   .upper_bound = 1.3, .lower_bound = 1, .result = 1,
+  },
+  // 6 - Big nanosecs
+  {.expected = { .tv_sec = 1, .tv_nsec = 0},
+   .observed = {.tv_sec = 0, .tv_nsec = 4000000},
+   .upper_bound = 1, .lower_bound = .001, .result = 1,
+  },
+  // 7 - In range Negative values
+  {.expected = { .tv_sec = -1, .tv_nsec = 0},
+   .observed = {.tv_sec = -1, .tv_nsec = 0},
+   .upper_bound = 1, .lower_bound = 1, .result = 1,
+  },
+  // 8 - Out of range Negative values
+  {.expected = { .tv_sec = -1, .tv_nsec = 0},
+   .observed = {.tv_sec = -1, .tv_nsec = 0},
+   .upper_bound = -1, .lower_bound = -1, .result = 0,
+  },
+  // 9 - Negative values with negative nanosecs
+  {.expected = { .tv_sec = -1, .tv_nsec = 0},
+   .observed = {.tv_sec = -1, .tv_nsec = -2000},
+   .upper_bound = 1, .lower_bound = 1, .result = 0,
+  },
+  // 10 - Strict bounds
+  {.expected = { .tv_sec = -1, .tv_nsec = 0},
+   .observed = {.tv_sec = -1, .tv_nsec = -20000},
+   .upper_bound = 1.00002, .lower_bound = 1.0000191, .result = 1,
+  },
+  // 11 - Strict bounds with loose upper bound
+  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
+   .observed = {.tv_sec = 1, .tv_nsec = 30000},
+   .upper_bound = 1.0000100000, .lower_bound = 1.0000099998, .result = 1,
+  },
+  // 12 - Strict bounds with loose lower bound
+  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
+   .observed = {.tv_sec = 1, .tv_nsec = 30000},
+   .upper_bound = 1.0000099999, .lower_bound = 1.00000999979, .result = 1,
+  },
+  // 13 - Strict bounds highest precision
+  {.expected = { .tv_sec = 1, .tv_nsec = 20000},
+   .observed = {.tv_sec = 1, .tv_nsec = 30000},
+   .upper_bound = 1.00000999980001, .lower_bound = 1.00000999979999, .result = 1,
+  },
+  /* Maximum/Minimum long values  */
+  // 14
+  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
+   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX -1},
+   .upper_bound = 1, .lower_bound = .9, .result = 1,
+  },
+  // 15
+  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
+   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
+   .upper_bound = 1, .lower_bound = 1, .result = 1,
+  },
+  // 16
+  {.expected = { .tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
+   .observed = {.tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
+   .upper_bound = 1, .lower_bound = 1, .result = 0,
+  },
+  // 17
+  {.expected = { .tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
+   .observed = {.tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
+   .upper_bound = 1, .lower_bound = 1, .result = 1,
+  },
+  // 18
+  {.expected = { .tv_sec = LONG_MIN, .tv_nsec = LONG_MIN},
+   .observed = {.tv_sec = LONG_MAX, .tv_nsec = LONG_MAX},
+   .upper_bound = 1, .lower_bound = 1, .result = 0,
+  }
+};
+
+static int
+do_test (void)
+{
+  int i = 0;
+  int ntests = sizeof (ns_cases) / sizeof (ns_cases);
+
+  for (i = 0; i < ntests; i++)
+    {
+      TEST_COMPARE (support_timespec_ns (ns_cases[i].time),
+		    ns_cases[i].time_ns);
+    }
+
+  ntests = sizeof (norm_cases) / sizeof (norm_cases);
+  struct timespec result;
+  for (i = 0; i < ntests; i++)
+    {
+      result = support_timespec_normalize (norm_cases[i].time);
+      TEST_COMPARE (norm_cases[i].norm.tv_sec, result.tv_sec);
+      TEST_COMPARE (norm_cases[i].norm.tv_nsec, result.tv_nsec);
+    }
+
+  ntests = sizeof (check_cases) / sizeof (check_cases);
+  for (i = 0; i < ntests; i++)
+    {
+      TEST_COMPARE (support_timespec_check_in_range
+		    (check_cases[i].expected, check_cases[i].observed,
+		     check_cases[i].lower_bound,
+		     check_cases[i].upper_bound), check_cases[i].result);
+    }
+  return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/time/tst-cpuclock1.c b/time/tst-cpuclock1.c
index 0120906f23..f9eb054f89 100644
--- a/time/tst-cpuclock1.c
+++ b/time/tst-cpuclock1.c
@@ -26,6 +26,7 @@
 #include <signal.h>
 #include <stdint.h>
 #include <sys/wait.h>
+#include <support/timespec.h>
 
 /* This function is intended to rack up both user and system time.  */
 static void
@@ -155,16 +156,11 @@ do_test (void)
   printf ("live PID %d after sleep => %ju.%.9ju\n",
 	  child, (uintmax_t) after.tv_sec, (uintmax_t) after.tv_nsec);
 
-  struct timespec diff = { .tv_sec = after.tv_sec - before.tv_sec,
-			   .tv_nsec = after.tv_nsec - before.tv_nsec };
-  if (diff.tv_nsec < 0)
-    {
-      --diff.tv_sec;
-      diff.tv_nsec += 1000000000;
-    }
-  if (diff.tv_sec != 0
-      || diff.tv_nsec > 600000000
-      || diff.tv_nsec < 100000000)
+  /* The bound values are empirically defined by testing this code over high cpu
+     usage and different nice values.  */
+  struct timespec diff = timespec_sub (support_timespec_normalize (after),
+				       support_timespec_normalize (before));
+  if (!support_timespec_check_in_range (sleeptime, diff, .4,  1.1))
     {
       printf ("before - after %ju.%.9ju outside reasonable range\n",
 	      (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
@@ -194,19 +190,14 @@ do_test (void)
 	}
       else
 	{
-	  struct timespec d = { .tv_sec = afterns.tv_sec - after.tv_sec,
-				.tv_nsec = afterns.tv_nsec - after.tv_nsec };
-	  if (d.tv_nsec < 0)
-	    {
-	      --d.tv_sec;
-	      d.tv_nsec += 1000000000;
-	    }
-	  if (d.tv_sec > 0
-	      || d.tv_nsec < sleeptime.tv_nsec
-	      || d.tv_nsec > sleeptime.tv_nsec * 2)
+        /* The bound values are empirically defined by testing this code over
+           high cpu usage and different nice values.  */
+	  diff = timespec_sub (support_timespec_normalize (afterns),
+			       support_timespec_normalize (after));
+	  if (!support_timespec_check_in_range (sleeptime, diff, .9, 1.2))
 	    {
 	      printf ("nanosleep time %ju.%.9ju outside reasonable range\n",
-		      (uintmax_t) d.tv_sec, (uintmax_t) d.tv_nsec);
+		      (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
 	      result = 1;
 	    }
 	}
@@ -240,15 +231,12 @@ do_test (void)
   /* Should be close to 0.6.  */
   printf ("dead PID %d => %ju.%.9ju\n",
 	  child, (uintmax_t) dead.tv_sec, (uintmax_t) dead.tv_nsec);
-
-  diff.tv_sec = dead.tv_sec - after.tv_sec;
-  diff.tv_nsec = dead.tv_nsec - after.tv_nsec;
-  if (diff.tv_nsec < 0)
-    {
-      --diff.tv_sec;
-      diff.tv_nsec += 1000000000;
-    }
-  if (diff.tv_sec != 0 || diff.tv_nsec > 200000000)
+  /* The bound values are empirically defined by testing this code over high cpu
+     usage and different nice values.  */
+  diff = timespec_sub (support_timespec_normalize (dead),
+		       support_timespec_normalize (after));
+  sleeptime.tv_nsec = 100000000;
+  if (!support_timespec_check_in_range (sleeptime, diff, .9, 1.2))
     {
       printf ("dead - after %ju.%.9ju outside reasonable range\n",
 	      (uintmax_t) diff.tv_sec, (uintmax_t) diff.tv_nsec);
-- 
2.20.1