* [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
@ 2022-06-22 6:01 Alexandre Oliva
2022-06-22 6:22 ` Sebastian Huber
0 siblings, 1 reply; 9+ messages in thread
From: Alexandre Oliva @ 2022-06-22 6:01 UTC (permalink / raw)
To: gcc-patches, libstdc++
On rtems under qemu, the frequently-interrupted nanosleep ends up
sleeping shorter than expected, by a margin of less than 0,3%.
I figured failing the library test over a system (emulator?) bug is
undesirable, so I put in some tolerance for the drift.
Regstrapped on x86_64-linux-gnu, also tested with a cross to
aarch64-rtems6. Ok to install?
PS: I see nothing wrong with the implementation of clock_nanosleep (used
by nanosleep) on rtems6 that could cause it to wake up too early. I
suspect some artifact of the emulation environment.
for libstdc++-v3/ChangeLog
* testsuite/30_threads/this_thread/60421.cc: Tolerate a
slightly early wakeup.
---
.../testsuite/30_threads/this_thread/60421.cc | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
index 12dbeba1cc492..f3a5af453c4ad 100644
--- a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
+++ b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
@@ -51,9 +51,10 @@ test02()
std::thread t([&result, &sleeping] {
auto start = std::chrono::system_clock::now();
auto time = std::chrono::seconds(3);
+ auto tolerance = std::chrono::milliseconds(10);
sleeping = true;
std::this_thread::sleep_for(time);
- result = std::chrono::system_clock::now() >= (start + time);
+ result = std::chrono::system_clock::now() + tolerance >= (start + time);
sleeping = false;
});
while (!sleeping)
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-22 6:01 [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep Alexandre Oliva
@ 2022-06-22 6:22 ` Sebastian Huber
2022-06-22 8:55 ` Sebastian Huber
0 siblings, 1 reply; 9+ messages in thread
From: Sebastian Huber @ 2022-06-22 6:22 UTC (permalink / raw)
To: Alexandre Oliva, gcc-patches, libstdc++, RTEMS
On 22/06/2022 08:01, Alexandre Oliva via Gcc-patches wrote:
>
> On rtems under qemu, the frequently-interrupted nanosleep ends up
> sleeping shorter than expected, by a margin of less than 0,3%.
>
> I figured failing the library test over a system (emulator?) bug is
> undesirable, so I put in some tolerance for the drift.
>
> Regstrapped on x86_64-linux-gnu, also tested with a cross to
> aarch64-rtems6. Ok to install?
>
> PS: I see nothing wrong with the implementation of clock_nanosleep (used
> by nanosleep) on rtems6 that could cause it to wake up too early. I
> suspect some artifact of the emulation environment.
>
>
> for libstdc++-v3/ChangeLog
>
> * testsuite/30_threads/this_thread/60421.cc: Tolerate a
> slightly early wakeup.
> ---
> .../testsuite/30_threads/this_thread/60421.cc | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
> index 12dbeba1cc492..f3a5af453c4ad 100644
> --- a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
> +++ b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
> @@ -51,9 +51,10 @@ test02()
> std::thread t([&result, &sleeping] {
> auto start = std::chrono::system_clock::now();
> auto time = std::chrono::seconds(3);
> + auto tolerance = std::chrono::milliseconds(10);
> sleeping = true;
> std::this_thread::sleep_for(time);
> - result = std::chrono::system_clock::now() >= (start + time);
> + result = std::chrono::system_clock::now() + tolerance >= (start + time);
> sleeping = false;
> });
> while (!sleeping)
This looks like a bug in RTEMS or the BSP for the test platform. I would
first investigate this and then change the test which looks all right to me.
--
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax: +49-89-18 94 741 - 08
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Unsere Datenschutzerklärung finden Sie hier:
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^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-22 6:22 ` Sebastian Huber
@ 2022-06-22 8:55 ` Sebastian Huber
2022-06-23 0:15 ` Alexandre Oliva
2022-06-23 0:19 ` Alexandre Oliva
0 siblings, 2 replies; 9+ messages in thread
From: Sebastian Huber @ 2022-06-22 8:55 UTC (permalink / raw)
To: Alexandre Oliva, gcc-patches, libstdc++, RTEMS
On 22/06/2022 08:22, Sebastian Huber wrote:
> On 22/06/2022 08:01, Alexandre Oliva via Gcc-patches wrote:
>>
>> On rtems under qemu, the frequently-interrupted nanosleep ends up
>> sleeping shorter than expected, by a margin of less than 0,3%.
>>
>> I figured failing the library test over a system (emulator?) bug is
>> undesirable, so I put in some tolerance for the drift.
>>
>> Regstrapped on x86_64-linux-gnu, also tested with a cross to
>> aarch64-rtems6. Ok to install?
>>
>> PS: I see nothing wrong with the implementation of clock_nanosleep (used
>> by nanosleep) on rtems6 that could cause it to wake up too early. I
>> suspect some artifact of the emulation environment.
>>
>>
>> for libstdc++-v3/ChangeLog
>>
>> * testsuite/30_threads/this_thread/60421.cc: Tolerate a
>> slightly early wakeup.
>> ---
>> .../testsuite/30_threads/this_thread/60421.cc | 3 ++-
>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
>> b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
>> index 12dbeba1cc492..f3a5af453c4ad 100644
>> --- a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
>> +++ b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
>> @@ -51,9 +51,10 @@ test02()
>> std::thread t([&result, &sleeping] {
>> auto start = std::chrono::system_clock::now();
>> auto time = std::chrono::seconds(3);
>> + auto tolerance = std::chrono::milliseconds(10);
>> sleeping = true;
>> std::this_thread::sleep_for(time);
>> - result = std::chrono::system_clock::now() >= (start + time);
>> + result = std::chrono::system_clock::now() + tolerance >= (start +
>> time);
>> sleeping = false;
>> });
>> while (!sleeping)
>
> This looks like a bug in RTEMS or the BSP for the test platform. I would
> first investigate this and then change the test which looks all right to
> me.
This is a problem in RTEMS. RTEMS uses the FreeBSD timecounters to
maintain CLOCK_REALTIME and provides two methods to get the time in a
coarse and fine resolution. The std::chrono::system_clock::now() uses
the fine resolution (higher overhead). The clock_nanosleep() uses the
coarse resolution which may give a time before now().
--
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax: +49-89-18 94 741 - 08
Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-22 8:55 ` Sebastian Huber
@ 2022-06-23 0:15 ` Alexandre Oliva
2022-06-23 0:19 ` Alexandre Oliva
1 sibling, 0 replies; 9+ messages in thread
From: Alexandre Oliva @ 2022-06-23 0:15 UTC (permalink / raw)
To: Sebastian Huber; +Cc: gcc-patches, libstdc++, RTEMS
On Jun 22, 2022, Sebastian Huber <sebastian.huber@embedded-brains.de> wrote:
> The clock_nanosleep() uses the coarse resolution
Thanks for looking into this. So, is it missing a rounding-up to ensure
the sleep time is >= the requested time, or is it even more elaborate
than that?
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-22 8:55 ` Sebastian Huber
2022-06-23 0:15 ` Alexandre Oliva
@ 2022-06-23 0:19 ` Alexandre Oliva
2022-06-23 6:44 ` Sebastian Huber
1 sibling, 1 reply; 9+ messages in thread
From: Alexandre Oliva @ 2022-06-23 0:19 UTC (permalink / raw)
To: Sebastian Huber; +Cc: gcc-patches, libstdc++, RTEMS
On Jun 22, 2022, Sebastian Huber <sebastian.huber@embedded-brains.de> wrote:
> The clock_nanosleep() uses the coarse resolution which may give a time
> before now().
Uhh, sorry, hit send too early.
I also meant to ask whether you'd like me to file an RTEMS ticket about
this issue.
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-23 0:19 ` Alexandre Oliva
@ 2022-06-23 6:44 ` Sebastian Huber
2022-06-23 7:27 ` Sebastian Huber
0 siblings, 1 reply; 9+ messages in thread
From: Sebastian Huber @ 2022-06-23 6:44 UTC (permalink / raw)
To: Alexandre Oliva; +Cc: gcc-patches, libstdc++, RTEMS
On 23/06/2022 02:19, Alexandre Oliva wrote:
> On Jun 22, 2022, Sebastian Huber<sebastian.huber@embedded-brains.de> wrote:
>
>> The clock_nanosleep() uses the coarse resolution which may give a time
>> before now().
> Uhh, sorry, hit send too early.
>
> I also meant to ask whether you'd like me to file an RTEMS ticket about
> this issue.
I already created a ticket for this and work on it:
http://devel.rtems.org/ticket/4669
--
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax: +49-89-18 94 741 - 08
Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-23 6:44 ` Sebastian Huber
@ 2022-06-23 7:27 ` Sebastian Huber
2022-06-23 11:33 ` Alexandre Oliva
0 siblings, 1 reply; 9+ messages in thread
From: Sebastian Huber @ 2022-06-23 7:27 UTC (permalink / raw)
To: Alexandre Oliva; +Cc: gcc-patches, libstdc++, RTEMS
On 23/06/2022 08:44, Sebastian Huber wrote:
> On 23/06/2022 02:19, Alexandre Oliva wrote:
>> On Jun 22, 2022, Sebastian Huber<sebastian.huber@embedded-brains.de>
>> wrote:
>>
>>> The clock_nanosleep() uses the coarse resolution which may give a time
>>> before now().
>> Uhh, sorry, hit send too early.
>>
>> I also meant to ask whether you'd like me to file an RTEMS ticket about
>> this issue.
>
> I already created a ticket for this and work on it:
>
> http://devel.rtems.org/ticket/4669
This problem should be fixed now in the RTEMS master branch. I had to
adjust the test case so that it works in a system with only one processor:
while (!sleeping)
{
// Wait for the thread to start sleeping.
std::this_thread::yield();
}
--
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax: +49-89-18 94 741 - 08
Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-23 7:27 ` Sebastian Huber
@ 2022-06-23 11:33 ` Alexandre Oliva
2022-06-23 11:37 ` Sebastian Huber
0 siblings, 1 reply; 9+ messages in thread
From: Alexandre Oliva @ 2022-06-23 11:33 UTC (permalink / raw)
To: Sebastian Huber; +Cc: gcc-patches, libstdc++, RTEMS
On Jun 23, 2022, Sebastian Huber <sebastian.huber@embedded-brains.de> wrote:
> On 23/06/2022 08:44, Sebastian Huber wrote:
>> http://devel.rtems.org/ticket/4669
Thanks!
> This problem should be fixed now in the RTEMS master branch.
Double thanks! I've applied the patch, and I haven't seen the fails any
more. It's a little too soon to confirm it fixed, but the patch makes
plenty of sense.
> I had to adjust the test case so that it works in a system with only
> one processor:
*nod*, I ran into that myself, and IIRC I've pushed an equivalent fix
earlier this week.
Anyway... I was considering this xfail patch before, and I wonder if it
would still be appropriate to install something like it, narrowed down
to rtems < 6.1, or if it would be better to let it fail noisily so that
people look it up, find the fix proper and merge it.
libstdc++: xfail nanosleep tests on rtems
Since it has been determined that nanosleep may return slightly too
early on RTEMS, due to clock resolution differences, expect
30_thread/this_thread tests that have detected too-early wakeups to
fail on RTEMS targets.
for libstdc++-v3/ChangeLog
* testsuite/30_threads/this_thread/60421.cc: xfail on RTEMS.
---
.../testsuite/30_threads/this_thread/60421.cc | 1 +
1 file changed, 1 insertion(+)
diff --git a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
index 12dbeba1cc492..4d86e0df20de4 100644
--- a/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
+++ b/libstdc++-v3/testsuite/30_threads/this_thread/60421.cc
@@ -23,6 +23,7 @@
// { dg-require-gthreads "" }
// { dg-require-time "" }
// { dg-require-sleep "" }
+// { dg-xfail-if "nanosleep may wake up too early" { *-*-rtems* } }
#include <thread>
#include <chrono>
--
Alexandre Oliva, happy hacker https://FSFLA.org/blogs/lxo/
Free Software Activist GNU Toolchain Engineer
Disinformation flourishes because many people care deeply about injustice
but very few check the facts. Ask me about <https://stallmansupport.org>
^ permalink raw reply [flat|nested] 9+ messages in thread
* Re: [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep
2022-06-23 11:33 ` Alexandre Oliva
@ 2022-06-23 11:37 ` Sebastian Huber
0 siblings, 0 replies; 9+ messages in thread
From: Sebastian Huber @ 2022-06-23 11:37 UTC (permalink / raw)
To: Alexandre Oliva; +Cc: gcc-patches, libstdc++, RTEMS
On 23/06/2022 13:33, Alexandre Oliva wrote:
> Anyway... I was considering this xfail patch before, and I wonder if it
> would still be appropriate to install something like it, narrowed down
> to rtems < 6.1, or if it would be better to let it fail noisily so that
> people look it up, find the fix proper and merge it.
I would not make it an xfail. It is now likely fixed and if someone uses
a broken RTEMS version getting an error message would be nice.
--
embedded brains GmbH
Herr Sebastian HUBER
Dornierstr. 4
82178 Puchheim
Germany
email: sebastian.huber@embedded-brains.de
phone: +49-89-18 94 741 - 16
fax: +49-89-18 94 741 - 08
Registergericht: Amtsgericht München
Registernummer: HRB 157899
Vertretungsberechtigte Geschäftsführer: Peter Rasmussen, Thomas Dörfler
Unsere Datenschutzerklärung finden Sie hier:
https://embedded-brains.de/datenschutzerklaerung/
^ permalink raw reply [flat|nested] 9+ messages in thread
end of thread, other threads:[~2022-06-23 11:37 UTC | newest]
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2022-06-22 6:01 [PATCH] libstdc++: 60241.cc: tolerate slightly shorter aggregate sleep Alexandre Oliva
2022-06-22 6:22 ` Sebastian Huber
2022-06-22 8:55 ` Sebastian Huber
2022-06-23 0:15 ` Alexandre Oliva
2022-06-23 0:19 ` Alexandre Oliva
2022-06-23 6:44 ` Sebastian Huber
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