AW: [PATCH] kern_tc.c: Update pps_event() for uniprocessor configurations

[Sebastian Huber]

On 01/06/2022 08:55, Gabriel.Moyano at dlr.de wrote:
>> On 30/05/2022 09:29, Gabriel Moyano wrote:
>>> Since pps->capgen is not used in uniprocessor configurations, there is
>>> no need to verified if it is equal to zero
>>>
>>> Update #2349
>>> ---
>>>    cpukit/score/src/kern_tc.c | 4 ++++
>>>    1 file changed, 4 insertions(+)
>>>
>>> diff --git a/cpukit/score/src/kern_tc.c b/cpukit/score/src/kern_tc.c
>>> index 92739d8edd..897f81511e 100644
>>> --- a/cpukit/score/src/kern_tc.c
>>> +++ b/cpukit/score/src/kern_tc.c
>>> @@ -2165,7 +2165,11 @@ pps_event(struct pps_state *pps, int event)
>>>    	if ((event & pps->ppsparam.mode) == 0)
>>>    		return;
>>>    	/* If the timecounter was wound up underneath us, bail out. */
>>> +#if defined(RTEMS_SMP)
>>>    	if (pps->capgen == 0 || pps->capgen !=
>>> +#else
>>> +	if (pps->capgen !=
>>> +#endif
>>>    	    atomic_load_acq_int(&pps->capth->th_generation))
>>>    		return;
>>>
>>
>> I think this fix is incomplete. What is with:
>>
>> void
>> pps_capture(struct pps_state *pps)
>> {
>> 	struct timehands *th;
>>
>> 	KASSERT(pps != NULL, ("NULL pps pointer in pps_capture"));
>> 	th = timehands;
>> 	pps->capgen = atomic_load_acq_int(&th->th_generation);
>> 	pps->capth = th;
>> #ifdef FFCLOCK
>> 	pps->capffth = fftimehands;
>> #endif
>> 	pps->capcount = th->th_counter->tc_get_timecount(th->th_counter);
>> 	atomic_thread_fence_acq();
>> 	if (pps->capgen != th->th_generation)
>> 		pps->capgen = 0;
>> }
>>
>> I don't know why there is this "if" in the code. I will ask on a FreeBSD mailing list.
>>
> 
> I think it is for the case that th_generation has changed in between saving the th and th_counter. If this happens pps->capgen is set to 0 and later pps_event() returns earlier. Since for uniprocessor th_generation equal to 0 is not used, I guess we can removed this if for those configurations

I asked on a FreeBSD mailing list:

https://lists.freebsd.org/archives/freebsd-hackers/2022-June/001165.html

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