calibrate intervals to avoid zero in futures poll test

calibrate intervals to avoid zero in futures poll test

[Alexandre Oliva]

We get occasional failures of 30_threads/future/members/poll.cc
on some platforms whose high resolution clock doesn't have such a high
resolution; wait_for_0 ends up as 0, and then some asserts fail as
intervals measured as longer than zero are tested for less than
several times zero.

This patch adds some calibration in the iteration count to set a
measurable base time interval with some additional margin.

Regstrapped on x86_64-linux-gnu, and also tested on
x-arm-wrs-vxworks7r2.  Ok to install?


for  libstdc++-v3/ChangeLog

	* testsuite/30_threads/future/members/poll.cc: Calibrate
	iteration count.
---
 .../testsuite/30_threads/future/members/poll.cc    |   33 +++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
index fff9bea899c90..7b41411a54386 100644
--- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
+++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
@@ -25,7 +25,7 @@
 #include <iostream>
 #include <testsuite_hooks.h>
 
-const int iterations = 200;
+int iterations = 200;
 
 using namespace std;
 
@@ -45,10 +45,41 @@ int main()
   promise<int> p;
   future<int> f = p.get_future();
 
+ start_over:
   auto start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
     f.wait_for(chrono::seconds(0));
   auto stop = chrono::high_resolution_clock::now();
+
+  /* We've run too few iterations for the clock resolution.
+     Attempt to calibrate it.  */
+  if (start == stop)
+    {
+      /* Loop until the clock advances, so that start is right after a
+	 time increment.  */
+      do
+	start = chrono::high_resolution_clock::now();
+      while (start == stop);
+      int i = 0;
+      /* Now until the clock advances again, so that stop is right
+	 after another time increment.  */
+      do
+	{
+	  f.wait_for(chrono::seconds(0));
+	  stop = chrono::high_resolution_clock::now();
+	  i++;
+	}
+      while (start == stop);
+      /* Got for some 10 cycles, but we're already past that and still
+	 get into the calibration loop, double the iteration count and
+	 try again.  */
+      if (iterations < i * 10)
+	iterations = i * 10;
+      else
+	iterations *= 2;
+      goto start_over;
+    }
+
   double wait_for_0 = print("wait_for(0s)", stop - start);
 
   start = chrono::high_resolution_clock::now();


-- 
Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
   Free Software Activist         GNU Toolchain Engineer
        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar

Re: calibrate intervals to avoid zero in futures poll test

[Alexandre Oliva]

On Jan  5, 2021, Alexandre Oliva <oliva@adacore.com> wrote:

> We get occasional failures of 30_threads/future/members/poll.cc
> on some platforms whose high resolution clock doesn't have such a high
> resolution; wait_for_0 ends up as 0, and then some asserts fail as
> intervals measured as longer than zero are tested for less than
> several times zero.

> This patch adds some calibration in the iteration count to set a
> measurable base time interval with some additional margin.

> Regstrapped on x86_64-linux-gnu, and also tested on
> x-arm-wrs-vxworks7r2.  Ok to install?

Ping?

https://gcc.gnu.org/pipermail/gcc-patches/2021-January/562796.html

> for  libstdc++-v3/ChangeLog

> 	* testsuite/30_threads/future/members/poll.cc: Calibrate
> 	iteration count.

-- 
Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
   Free Software Activist         GNU Toolchain Engineer
        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar

Re: calibrate intervals to avoid zero in futures poll test

[Jonathan Wakely]

On 05/01/21 04:44 -0300, Alexandre Oliva wrote:
>
>We get occasional failures of 30_threads/future/members/poll.cc
>on some platforms whose high resolution clock doesn't have such a high
>resolution; wait_for_0 ends up as 0, and then some asserts fail as
>intervals measured as longer than zero are tested for less than
>several times zero.
>
>This patch adds some calibration in the iteration count to set a
>measurable base time interval with some additional margin.
>
>Regstrapped on x86_64-linux-gnu, and also tested on
>x-arm-wrs-vxworks7r2.  Ok to install?
>
>
>for  libstdc++-v3/ChangeLog
>
>	* testsuite/30_threads/future/members/poll.cc: Calibrate
>	iteration count.
>---
> .../testsuite/30_threads/future/members/poll.cc    |   33 +++++++++++++++++++-
> 1 file changed, 32 insertions(+), 1 deletion(-)
>
>diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
>index fff9bea899c90..7b41411a54386 100644
>--- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
>+++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
>@@ -25,7 +25,7 @@
> #include <iostream>
> #include <testsuite_hooks.h>
>
>-const int iterations = 200;
>+int iterations = 200;
>
> using namespace std;
>
>@@ -45,10 +45,41 @@ int main()
>   promise<int> p;
>   future<int> f = p.get_future();
>
>+ start_over:
>   auto start = chrono::high_resolution_clock::now();
>   for(int i = 0; i < iterations; i++)
>     f.wait_for(chrono::seconds(0));
>   auto stop = chrono::high_resolution_clock::now();
>+
>+  /* We've run too few iterations for the clock resolution.
>+     Attempt to calibrate it.  */
>+  if (start == stop)
>+    {
>+      /* Loop until the clock advances, so that start is right after a
>+	 time increment.  */
>+      do
>+	start = chrono::high_resolution_clock::now();
>+      while (start == stop);
>+      int i = 0;
>+      /* Now until the clock advances again, so that stop is right
>+	 after another time increment.  */
>+      do
>+	{
>+	  f.wait_for(chrono::seconds(0));
>+	  stop = chrono::high_resolution_clock::now();
>+	  i++;
>+	}
>+      while (start == stop);
>+      /* Got for some 10 cycles, but we're already past that and still

I can't parse "Got for some 10 cycles". If that's just a typo that I'm
failing to spot ("good for"?) please fix and push the patch.

The patch is fine apart from me being unable to understand this
comment.

>+	 get into the calibration loop, double the iteration count and
>+	 try again.  */
>+      if (iterations < i * 10)
>+	iterations = i * 10;
>+      else
>+	iterations *= 2;
>+      goto start_over;
>+    }
>+
>   double wait_for_0 = print("wait_for(0s)", stop - start);
>
>   start = chrono::high_resolution_clock::now();
>
>
>-- 
>Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
>   Free Software Activist         GNU Toolchain Engineer
>        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar
>

Re: calibrate intervals to avoid zero in futures poll test

[Alexandre Oliva]

On Jan 14, 2021, Jonathan Wakely <jwakely@redhat.com> wrote:

>> +      /* Got for some 10 cycles, but we're already past that and still

> I can't parse "Got for some 10 cycles". If that's just a typo

Yeah, I meant "Go for ... but if ..." and managed to double-mangle it.
Thanks for spotting it.  Here's the patch I'm installing, with the typos
fixed.  Thanks!


calibrate intervals to avoid zero in futures poll test

From: Alexandre Oliva <oliva@adacore.com>

We get occasional failures of 30_threads/future/members/poll.cc
on some platforms whose high resolution clock doesn't have such a high
resolution; wait_for_0 ends up as 0, and then some asserts fail as
intervals measured as longer than zero are tested for less than
several times zero.

This patch adds some calibration in the iteration count to set a
measurable base time interval with some additional margin.


for  libstdc++-v3/ChangeLog

	* testsuite/30_threads/future/members/poll.cc: Calibrate
	iteration count.
---
 .../testsuite/30_threads/future/members/poll.cc    |   33 +++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
index 91f685b172d73..133dae15ac471 100644
--- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
+++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
@@ -25,7 +25,7 @@
 #include <iostream>
 #include <testsuite_hooks.h>
 
-const int iterations = 200;
+int iterations = 200;
 
 using namespace std;
 
@@ -45,10 +45,41 @@ int main()
   promise<int> p;
   future<int> f = p.get_future();
 
+ start_over:
   auto start = chrono::high_resolution_clock::now();
   for(int i = 0; i < iterations; i++)
     f.wait_for(chrono::seconds(0));
   auto stop = chrono::high_resolution_clock::now();
+
+  /* We've run too few iterations for the clock resolution.
+     Attempt to calibrate it.  */
+  if (start == stop)
+    {
+      /* Loop until the clock advances, so that start is right after a
+	 time increment.  */
+      do
+	start = chrono::high_resolution_clock::now();
+      while (start == stop);
+      int i = 0;
+      /* Now until the clock advances again, so that stop is right
+	 after another time increment.  */
+      do
+	{
+	  f.wait_for(chrono::seconds(0));
+	  stop = chrono::high_resolution_clock::now();
+	  i++;
+	}
+      while (start == stop);
+      /* Go for some 10 cycles, but if we're already past that and
+	 still get into the calibration loop, double the iteration
+	 count and try again.  */
+      if (iterations < i * 10)
+	iterations = i * 10;
+      else
+	iterations *= 2;
+      goto start_over;
+    }
+
   double wait_for_0 = print("wait_for(0s)", stop - start);
 
   start = chrono::high_resolution_clock::now();


-- 
Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
   Free Software Activist         GNU Toolchain Engineer
        Vim, Vi, Voltei pro Emacs -- GNUlius Caesar

Re: calibrate intervals to avoid zero in futures poll test

[Christophe Lyon]

On Thu, 14 Jan 2021 at 19:57, Alexandre Oliva <oliva@adacore.com> wrote:
>
> On Jan 14, 2021, Jonathan Wakely <jwakely@redhat.com> wrote:
>
> >> +      /* Got for some 10 cycles, but we're already past that and still
>
> > I can't parse "Got for some 10 cycles". If that's just a typo
>
> Yeah, I meant "Go for ... but if ..." and managed to double-mangle it.
> Thanks for spotting it.  Here's the patch I'm installing, with the typos
> fixed.  Thanks!
>
>
> calibrate intervals to avoid zero in futures poll test
>
> From: Alexandre Oliva <oliva@adacore.com>
>
> We get occasional failures of 30_threads/future/members/poll.cc
> on some platforms whose high resolution clock doesn't have such a high
> resolution; wait_for_0 ends up as 0, and then some asserts fail as
> intervals measured as longer than zero are tested for less than
> several times zero.
>
> This patch adds some calibration in the iteration count to set a
> measurable base time interval with some additional margin.
>

Seeing such random errors when testing arm target under qemu
on shared servers. I noticed several such errors on gcc-testresults, too.

So I guess this is a ping for this patch, to clear this noise in the results?

Thanks,

Christophe


>
> for  libstdc++-v3/ChangeLog
>
>         * testsuite/30_threads/future/members/poll.cc: Calibrate
>         iteration count.
> ---
>  .../testsuite/30_threads/future/members/poll.cc    |   33 +++++++++++++++++++-
>  1 file changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
> index 91f685b172d73..133dae15ac471 100644
> --- a/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
> +++ b/libstdc++-v3/testsuite/30_threads/future/members/poll.cc
> @@ -25,7 +25,7 @@
>  #include <iostream>
>  #include <testsuite_hooks.h>
>
> -const int iterations = 200;
> +int iterations = 200;
>
>  using namespace std;
>
> @@ -45,10 +45,41 @@ int main()
>    promise<int> p;
>    future<int> f = p.get_future();
>
> + start_over:
>    auto start = chrono::high_resolution_clock::now();
>    for(int i = 0; i < iterations; i++)
>      f.wait_for(chrono::seconds(0));
>    auto stop = chrono::high_resolution_clock::now();
> +
> +  /* We've run too few iterations for the clock resolution.
> +     Attempt to calibrate it.  */
> +  if (start == stop)
> +    {
> +      /* Loop until the clock advances, so that start is right after a
> +        time increment.  */
> +      do
> +       start = chrono::high_resolution_clock::now();
> +      while (start == stop);
> +      int i = 0;
> +      /* Now until the clock advances again, so that stop is right
> +        after another time increment.  */
> +      do
> +       {
> +         f.wait_for(chrono::seconds(0));
> +         stop = chrono::high_resolution_clock::now();
> +         i++;
> +       }
> +      while (start == stop);
> +      /* Go for some 10 cycles, but if we're already past that and
> +        still get into the calibration loop, double the iteration
> +        count and try again.  */
> +      if (iterations < i * 10)
> +       iterations = i * 10;
> +      else
> +       iterations *= 2;
> +      goto start_over;
> +    }
> +
>    double wait_for_0 = print("wait_for(0s)", stop - start);
>
>    start = chrono::high_resolution_clock::now();
>
>
> --
> Alexandre Oliva, happy hacker  https://FSFLA.org/blogs/lxo/
>    Free Software Activist         GNU Toolchain Engineer
>         Vim, Vi, Voltei pro Emacs -- GNUlius Caesar