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SubjectRe: [PATCH] dynamic tick patch
Tony Lindgren wrote:
> * George Anzinger <george@mvista.com> [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@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/

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