Re: [Xenomai-core] ns vs. tsc as internal timer base

[Philippe Gerum <rpm@xenomai.org>]

Jim Cromie wrote:
> Philippe Gerum wrote:
> 
>> Gilles Chanteperdrix wrote:
>>
>>> Philippe Gerum wrote:
>>>  > Redone the check here on a Centrino 1.6Mhz, and still have roughly 
>>> x20  > improvement (a bit better actually). I'm using Debian/sarge 
>>> gcc 3.3.5.
>>>
>>> I think I remember that Pentium M has a much shorter mull instruction
>>> than other processors of the family.
>>>
>>
>> That would explain. Anyway, as John Stulz put it:
>> "math is hard, lets go shopping!"
>>
> 
> Heh.  Appropriate that his name (Stultz) comes up here, as his 
> generic-time (GTOD)
> patchset looks headed for 2.6.18, bringing with it a full re-working
> of linux timers / timeofday.  IN this new world, time is kept on 
> free-running counters.
> 
> Ive been running this patchset on my soekris for some time, since
> GTOD detects that the TSC counts slowly, calls it insane, and does timing
> with the PIT.
> 
> With GTOD, writing a new clocksource driver is easy, enough so I could 
> do it.
> My clocksource patch uses the 27 mhz timer on the Geode CPU.
> Once the TSC is de-rated, mine becomes the best clocksource, and GTOD 
> switches to it.
> 
> All of which is to say ..
> new mainline code is coming, should this current rework notion wait,
> given that its will all need revisited again later
> 

Clearly yes, since this is going to impact Adeos too. GTOD is going to 
fiddle with the PIT channels in a way Adeos needs to be aware of, in 
order for the client RTOS to reuse such timer. Added to the flow of 
other core changes planned for 2.6.18, this is likely going to be funky.

"Find wall. Beat head against same."

-- 

Philippe.