Re: [PATCH] dynamic tick patch

[George Anzinger]

Tony Lindgren wrote:
> * George Anzinger <george@xxxxxxxxxx> [050119 15:00]:
>
> > I don't think you will ever get good time if you EVER reprogramm the PIT.  
> > That is why the VST patch on sourceforge does NOT touch the PIT, it only 
> > turns off the interrupt by interrupting the interrupt path (not changing 
> > the PIT).  This allows the PIT to be the "gold standard" in time that it is 
> > designed to be.  The wake up interrupt, then needs to come from an 
> > independent timer.  My patch requires a local APIC for this.  Patch is 
> > available at http://sourceforge.net/projects/high-res-timers/
>
>
> Well on my test systems I have pretty good accurate time. But I agree,
> PIT is not the best option for interrupt. It should be possible to use
> other interrupt sources as well.
>
> It should not matter where the timer interrupt comes from, as long as 
> it comes when programmed. Updating time should be separate from timer
> interrupts. Currently we have a problem where time is tied to the
> timer interrupt.

In the HRT code time is most correctly stated as wall_time + 
get_arch_cycles_since(wall_jiffies) (plus conversion or two:)).  This is some 
what removed from the tick interrupt, but is resynced to that interrupt more or 
less each interrupt.

A second issue is trying to get the jiffies update as close to the run of the 
timer list as possible.  Without this we have no hope of high res timers.

--
George Anzinger   george@xxxxxxxxxx
High-res-timers:  http://sourceforge.net/projects/high-res-timers/

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