Re: Detecting PREEMPT_RT

[Carsten Emde <C.Emde@osadl.org>]

John,

>>>> Unfortunately, this wiki article is old and unmaintained. You're
>>>> probably right to be a bit suspicious when checking for the "-rt" suffix
>>>> of the kernel release (uname -r). But looking for the occurrence of
>>>> "PREEMPT RT" in the kernel version (uname -v) should work. An
>>>> application may use the system call uname() and check the version
>>>> element of the utsname structure.
>>> the utsname.version string match is fine, however:
>>>> In addition you may want to make sure the system has
>>>> high-resolution
>>> timers. If so, the timers in /proc/timer_list have ".resolution: 1
>>> nsecs". An application may use the function check_timer() from
>>> cyclictest for this purpose:
>>>> static int check_timer(void)
>>>> {
>>>>    struct timespec ts;
>>>>
>>>>    if (clock_getres(CLOCK_MONOTONIC, &ts))
>>>>      return 1;
>>>>
>>>>    return (ts.tv_sec != 0 || ts.tv_nsec != 1);
>>>> }
>>>
>>> Just tried this on a generic kernel (2.6.32-45-generic #102-Ubuntu
>>> SMP Wed Jan 2 21:53:06 UTC 2013 i686 GNU/Linux) and I get ts.tv_sec == 0
>>> and ts.tv_nsec == 1, so it looks this cant be used to tell an RT_PREEMPT
>>> from a vanilla kernel
>> I meant boolean AND when I said "In addition".
> Oh, I interpreted the timer check not as a PREEMPT_RT check, but a
> separate check for timers, which we must confirm are available before
> driving heavy machinery.
> So, if utsname.version contains "PREEMPT RT", then load the preempt-rt
> module.  Once the module is loaded, from an init() function, run sanity
> checks, including the clock_getres check above.  Is that about right?
Yes. Sounds good to me.

	-Carsten.