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Date: Wed, 03 Dec 2008 12:22:34 +0100
From: Wolfgang Grandegger <wg@domain.hid>
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Subject: Re: [Xenomai-help] pthread cancelation and scheduling magics
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Philippe Gerum wrote:
> Wolfgang Grandegger wrote:
>> Gilles Chanteperdrix wrote:
>>> Wolfgang Grandegger wrote:
>>>> Gilles Chanteperdrix wrote:
>>>>> For architectures with a high-resolution counter,
>>>>> clock_gettime(CLOCK_MONOTONIC) is a xenomai service which uses the
>>>>> counter and does not issue any syscall, this includes arm unless you
>>>>> configured xenomai with --enable-arm-arch=generic or with
>>>>> --disable-arm-tsc, and this probably includes powerpc.
>>>>>
>>>> clock_gettime() is wrapped to __wrap_clock_gettime(), which does a syscall:
>>>>
>>>> http://www.rts.uni-hannover.de/xenomai/lxr/source/src/skins/posix/clock.c?v=SVN-trunk#058
>>>>
>>>> Have I missed something?
>>> Yes, read the code again.
>> I was aware of CONFIG_XENO_HW_DIRECT_TSC but didn't look it up correctly
>> :-(. It is set for my ARM  but not for my PowerPC system. Which explains
>> some differences.
>>
> 
> We do have direct TSC readings on powerpc as well by looking at the timebase
> register from userland, but this only applies to rt_native_tsc(), or
> clock_gettime() when using CLOCK_MONOTONIC in aperiodic mode.

Well, yes, and the code is  quite clear in this respect. I just did not
 search for CONFIG_XENO_HW_DIRECT_TSC carefully. Sorry for the snapshot.

Wolfgang.