Messages in this thread | | | Date | Wed, 19 Jan 2005 16:24:42 -0800 | From | George Anzinger <> | Subject | Re: [PATCH] dynamic tick patch |
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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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