Re: [LTP] [PATCH] open_posix_testsuite: Don't use clock_settime() to reset a CPU-time Clock

[Gui Jianfeng <guijianfeng@cn.fujitsu.com>]

Gui Jianfeng wrote:
> Garrett Cooper wrote:
>> On Sun, Nov 7, 2010 at 8:09 PM, Gui Jianfeng <guijianfeng@cn.fujitsu.com> wrote:
>>> Gui Jianfeng wrote:
>>>> This case is trying to set CPU-time clock(ID is returned by clock_getcpuclockid()) of
>>>> a specific process by calling clock_settime(). But Linux kernel doesn't allow to reset
>>>> a CPU-time clock of a specific process. Kernel returns -EPERM. So test fails.
>>>>
>>>> In "IEEE Std 1003.1, 2004 Edition", It's said as following:
>>>> If _POSIX_CPUTIME is defined, implementations shall support clock ID values obtained by
>>>> invoking clock_getcpuclockid(), which represent the CPU-time clock of a given process.
>>>> Implementations shall also support the special clockid_t value CLOCK_PROCESS_CPUTIME_ID,
>>>> which represents the CPU-time clock of the calling process when invoking one of the
>>>> clock_*() or timer_*() functions. For these clock IDs, the values returned by
>>>> clock_gettime() and specified by clock_settime() represent the amount of execution time
>>>> of the process associated with the clock. Changing the value of a CPU-time clock via
>>>> clock_settime() shall have no effect on the behavior of the sporadic server scheduling
>>>> policy.
>>>>
>>>> So the behaviour when changing the value of a CPU-time clock via clock_settime() is
>>>> operating system specific.
>>>>
>>>> We may change the test progress to stop using clock_settime(). Now, We just make use
>>>> of clock_gettime() instead to achieve the same test purpose.
>>>>
>>>> Signed-off-by: Gui Jianfeng <guijianfeng@cn.fujitsu.com>
>>> Hi Garrett,
>>>
>>> How do you think this fix?
>> The tort is the same in POSIX 2008.1. Taking out the chaff...
>>
>> a. If _POSIX_CPUTIME is defined, implementations shall support clock
>> ID values obtained by invoking clock_getcpuclockid(), which represent
>> the CPU-time clock of a given process.
>> b. Implementations shall also support the special clockid_t value
>> CLOCK_PROCESS_CPUTIME_ID, which represents the CPU-time clock of the
>> calling process when invoking one of the clock_*() or timer_*()
>> functions.
>> c. For these clock IDs, the values returned by clock_gettime() and
>> specified by clock_settime() represent the amount of execution time of
>> the process associated with the clock.
>>
>> Nowhere does it say that you can't set that clock. Try running the
>> test as root to see what you can do... if the test fails (even as
>> root), then Linux needs to be fixed to conform to POSIX.
> 
> POSIX also says that:
>   Changing the value of a CPU-time clock via clock_settime() shall have no effect 
>   on the behavior of the sporadic server scheduling policy.
> 
> IMHO, this means clock_settime() implementation is OS specific, is it?
> So, even if Linux fails to set this clock, it's just fine. Am i missing something?

Hi Garrett,

If you don't object, would you apply this patch?

Gui

> 
> Gui
> 
>> Also, try running the other tests I just added to see whether or not
>> the function call fails per POSIX's requirements.
>>
>> Thanks!
>> -Garrett
>>
> 
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