Re: [Adeos-main] [RFC][PATCH 2/2] x86: Add support for ipipe_get_irq_regs

[Philippe Gerum <rpm@xenomai.org>]

On Sat, 2010-06-05 at 22:48 +0200, Jan Kiszka wrote:
> Gilles Chanteperdrix wrote:
> > Jan Kiszka wrote:
> >> Philippe Gerum wrote:
> >>> On Thu, 2010-06-03 at 16:22 +0200, Jan Kiszka wrote:
> >>>> From: Jan Kiszka <jan.kiszka@domain.hid>
> >>>>
> >>>> Implement the x86 arch bits for ipipe_get_irq_regs support. This allows
> >>>> to drop __ipipe_tick_regs and use the new service instead.
> >>> I'm unsure whether this patch would actually replace __ipipe_tick_regs
> >>> properly, particularly regarding how the profiling code works.
> >> tick_regs are a "workaround", this approach appears to me way closer to
> >> how native works.
> > 
> > We do not want ipipe_tick_regs to work the way the native kernel works.
> > We want to fool the kernel by passing it the value of the registers at
> > the moment of the real timer tick so that its accounting works more or
> > less reliably. When the kernel used the real registers it got the
> > accounting wrong.
> 
> Right, though current tick_regs approach is not accurate either: the
> preempted task gets the full time slice accounted, neglecting the actual
> schedule inside the preempting domain.
> 

Indeed. This trade-off was made back in 2002.

> 
> Jan
> 
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-- 
Philippe.