Re: RT patch and arch/i386/kernel/time.c question

[Mathieu Desnoyers <compudj@krystal.dyndns.org>]

* Steven Rostedt (rostedt@goodmis.org) wrote:
> 
> On Tue, 7 Mar 2006, Serge Noiraud wrote:
> 
> > hi,
> >
> > 	I'm trying to port the LTTng patch over the rt20 and I got the following problem :
> > The LTTng patch try to modify the arch/i386/kernel/time.c file in which the
> > timer_interrupt function doesn't exist anymore.
> >
> > In which file / function could I try to patch the equivalent function ?
> >
> 
> The -rt patch uses the lastest stuff from Thomas Gleixner, John Stultz and
> of course Ingo Molnar.  The functions you are interested in, are in
> kernel/time/ directory.  Take a look at clockevents.c and perhaps
> handle_tick().  I'm not sure what LTTng is doing there, but this will give
> you a direction in which way to look.
> 
> -- Steve
> 

LTTng is updating its logical clock there. Note that this clock is only used on
architectures missing a synchronised CPU timestamp counter (NUMA and old i586).

If you have a fairly standard architecture (i686 with TSC available), this
combination of jiffies counter and logical clock is not used.

Look for where the xtime_lock seqlock is taken in the -rt patch : that's where
the logical clock should be updated.

Mathieu

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