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

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

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?

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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