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Posted to commits@nuttx.apache.org by GitBox <gi...@apache.org> on 2021/04/11 06:28:33 UTC
[GitHub] [incubator-nuttx] btashton opened a new issue #3516: CLOCKS_PER_SEC is not POSIX compliant
btashton opened a new issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516
NuttX defines `CLOCKS_PER_SEC` as:
```
#ifdef CONFIG_USEC_PER_TICK
# define CLK_TCK (1000000/CONFIG_USEC_PER_TICK)
# define CLOCKS_PER_SEC (1000000/CONFIG_USEC_PER_TICK)
#else
# define CLK_TCK (100)
# define CLOCKS_PER_SEC (100)
#endif
```
But the POSIX standard defines it as always one million.
https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
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[GitHub] [incubator-nuttx] patacongo commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817302335
>
>
> @patacongo do you have any thoughts on this one?
This implies that OpenGroup.org expects the system timer to ALWAYS have a resolution of 1 MSec. Just changing the the setting to a million would break all architectures. And, if all system timer APIs were modified to report / accept the time in "ticks" at a resolution of 1 MSec, then there were would be loss of functionality that is very important to an embedded system.
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[GitHub] [incubator-nuttx] patacongo edited a comment on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo edited a comment on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817350766
>
>
> Ah yes I see that the N1256 says nothing about this needing to be 1000000. Unfortunate that the open posix test suite asserts this value.
Then it must also be a POSIX error that the return value of clock() is incorrect: https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
But clock() would fail a POSIX test anyway because it is supposed to be the CPU time used by a process, not the elapsed time since reset.
Interestingly, the older CLK_TCK does not seem to have any required value.
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[GitHub] [incubator-nuttx] patacongo edited a comment on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo edited a comment on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817350766
>
>
> Ah yes I see that the N1256 says nothing about this needing to be 1000000. Unfortunate that the open posix test suite asserts this value.
Then it must also be a POSIX error that the return value of clock() is incorrect: https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
Interestingly, the older CLK_TCK does not seem to have any required value.
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[GitHub] [incubator-nuttx] btashton commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
btashton commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817349925
Ah yes I see that the N1256 says nothing about this needing to be 1000000. Unfortunate that the open posix test suite asserts this value.
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[GitHub] [incubator-nuttx] patacongo edited a comment on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo edited a comment on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817350766
>
>
> Ah yes I see that the N1256 says nothing about this needing to be 1000000. Unfortunate that the open posix test suite asserts this value.
Then it must also be a POSIX error that the return value of clock() is incorrect: https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
But clock() would fail a POSIX test anyway because it is supposed to be the CPU time used by a process, not the elapsed time since reset.
In general, I believe that we have to comply with POSIX requirements, whether we like them or not.
Interestingly, the older CLK_TCK does not seem to have any required value.
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[GitHub] [incubator-nuttx] xiaoxiang781216 commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817323019
From the thread:
```
The only thing the C99 N1256 standard draft says about CLOCKS_PER_SEC is that:
CLOCKS_PER_SEC which expands to an expression with type clock_t (described below) that is the number per second of the value returned by the clock function
```
And the quote from opengroup:
```
The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
```
The value different from 1000000 is acceptable.
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[GitHub] [incubator-nuttx] btashton commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
btashton commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817378907
My reading of the opengroup page is that it is OK if `CLOCKS_PER_SEC` is not 1M, as it is suppose to be the definition of C N1256 standard, it just usually is 1M. What is important is that `clock()` / `CLOCKS_PER_SEC` is gives to process duration. Because we are using `clock_systime_ticks` this is not correct.
My understanding is that we should to make clock() return the process ticks. It would be _nice_ if we made CLOCKS_PER_SEC be 1M, but it would be ideal to just hide this in the clock() interfaces and use a real CLOCKS_PER_SEC in the OS internals. This second bit I don't think is technically required.
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[GitHub] [incubator-nuttx] patacongo commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817360553
I see you closed this. Is that what we should do? It appears to be a real POSIX non-conformance problem.
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[GitHub] [incubator-nuttx] btashton edited a comment on issue #3516: clock() and CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
btashton edited a comment on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817378907
My reading of the opengroup page is that it is OK if `CLOCKS_PER_SEC` is not 1M, as it is suppose to be the definition of C N1256 standard (which has no requirement for this), it just usually is 1M. What is important is that `clock()` / `CLOCKS_PER_SEC` is gives to process duration. Because we are using `clock_systime_ticks` this is not correct.
My understanding is that we should to make clock() return the process ticks. It would be _nice_ if we made CLOCKS_PER_SEC be 1M, but it would be ideal to just hide this in the clock() interfaces and use a real CLOCKS_PER_SEC in the OS internals. This second bit I don't think is technically required.
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[GitHub] [incubator-nuttx] patacongo commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817350766
>
>
> Ah yes I see that the N1256 says nothing about this needing to be 1000000. Unfortunate that the open posix test suite asserts this value.
Then it must also be a POSIX error that the return value of clock() is incorrect: https://pubs.opengroup.org/onlinepubs/9699919799/functions/clock.html
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[GitHub] [incubator-nuttx] btashton commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
btashton commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817263658
@patacongo do you have any thoughts on this one?
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[GitHub] [incubator-nuttx] btashton closed issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
btashton closed issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516
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[GitHub] [incubator-nuttx] xiaoxiang781216 edited a comment on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
xiaoxiang781216 edited a comment on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817323019
From the thread:
```
The only thing the C99 N1256 standard draft says about CLOCKS_PER_SEC is that:
CLOCKS_PER_SEC which expands to an expression with type clock_t (described below) that is the number per second of the value returned by the clock function
```
And the quote from opengroup:
```
The functionality described on this reference page is aligned with the ISO C standard. Any conflict between the requirements described here and the ISO C standard is unintentional. This volume of POSIX.1-2017 defers to the ISO C standard.
```
A value different from 1000000 is acceptable.
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[GitHub] [incubator-nuttx] patacongo commented on issue #3516: CLOCKS_PER_SEC is not POSIX compliant
Posted by GitBox <gi...@apache.org>.
patacongo commented on issue #3516:
URL: https://github.com/apache/incubator-nuttx/issues/3516#issuecomment-817314170
You are not the only one confused: https://stackoverflow.com/questions/10455905/why-is-clocks-per-sec-not-the-actual-number-of-clocks-per-second
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