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Date: Wed, 16 Aug 2006 17:43:32 +0200
Subject: Re: [Xenomai-core] [RFC][PATCH 4/4] shorten overrun loops of periodic
	timers
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From: Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>
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	discussions\)" <xenomai.xenomai.org>
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To: Jan Kiszka <jan.kiszka@domain.hid>
Cc: xenomai-core <xenomai@xenomai.org>

Jan Kiszka wrote:
 > Gilles Chanteperdrix wrote:
 > > Jan Kiszka wrote:
 > >  > A simple patch, just like suggested by Gilles, to avoid looping over
 > >  > periodic xntimer handlers in case of overruns.
 > >  > 
 > >  > It saves the current TSC on loop entry and uses this value later when
 > >  > forwarding the timer. Is is the overhead of re-reading the TSC on all
 > >  > archs negligible and should we rather go that way?
 > > 
 > >  >(...)
 > >  > -				xntimerh_date(&timer->aplink) +=
 > >  > -				    nkpod->htimer.interval;
 > >  > +				while ((xntimerh_date(&timer->aplink) +=
 > >  > +				        nkpod->htimer.interval) < now);
 > > 
 > > I think you are patching the wrong addition, the one you are interested
 > > in is most probably the one at the bottom of xntimer_do_tick_aperiodic.
 > > 
 > 
 > Ouch, indeed. Guess I should start reading what I patch. Here comes a
 > second try.
 > 
 > I'm still in favour of saving the TSC instead of re-reading it.
 > Otherwise we would have to pave the code with #ifdefs for the case
 > xnarch_get_cpu_tsc() is slow for a specific setup. Not that nice, is it?

I am thinking again about this patch: some handlers need to be
rewritten, for example the posix timers handler, because the handler
relies on the fact that it is called for every timer expiry to compute
the overruns count. So maybe this patch should come with the addition of
an xntimer_getoverrun service that computes the overrun count using the
tsc ?

-- 


					    Gilles Chanteperdrix.