[Bug 2180] New: _TOD_Get_with_nanoseconds() is broken on SMP

[Sebastian Huber]

On 20/08/14 16:05, Joel Sherrill wrote:
>
> On 8/20/2014 8:59 AM, Sebastian Huber wrote:
>> On 20/08/14 15:53, Joel Sherrill wrote:
>>> On 8/20/2014 8:12 AM, Daniel Cederman wrote:
>>>>> Hi,
>>>>>
>>>>> We are currently experiencing this bug reported by Sebastian Huber and I
>>>>> could not find any discussion on it on the list. I'm guessing that the
>>>>> simple solution of moving the call to Clock_driver_support_at_tick() to
>>>>> the critical section of _TOD_Tickle_ticks() is not an acceptable
>>>>> solution, given that it would be a call from score to the BSP?
>>> I don't have a problem with it. Some documentation may need to be updated to
>>> reflect the environment in which the bsp hook is called but I think it
>>> is pretty
>>> obvious it is called when an accurate timestamp is wanted.
>> Its not that easy.  This Clock_driver_support_at_tick() is part of
>> clockdrv_shell.h.  What we need is a proper clock driver API.
>>
> Grrr.. I should have actually re-read the PR and not tried to remember
> the issue.
> Sorry. :(
>
> It looks like the entire sequence needs to be locked.  What that exposes is
> another matter.
>

The clock handling is entirely broken on SMP and not scalable.  Our clock 
infrastructure is only good enough for uni-processor systems, but even here the 
usage of nanosecond timestamps is suboptimal.  I would rather use something 
like the FreeBSD time hands:

http://phk.freebsd.dk/pubs/timecounter.pdf

Anyway I don't have a budget for this, so for the current ESA project I would 
disable the nanoseconds support in case this bug hurts.

-- 
Sebastian Huber, embedded brains GmbH

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