Re: [RFC][PATCH] i386 x86-64 Eliminate Local APIC timer interrupt

From: Zwane Mwaikambo
Date: Fri Apr 29 2005 - 20:12:04 EST

On Fri, 29 Apr 2005, Venkatesh Pallipadi wrote:

> Proposed Fix:
> Attached is a prototype patch, that tries to eliminate the dependency on
> local APIC timer for update_process_times(). The patch gets rid of Local APIC
> timer altogether. We use the timer interrupt (IRQ 0) configured in
> broadcast mode in IOAPIC instead (Doesn't work with 8259).
> As changing anything related to basic timer interrupt is a little bit risky,
> I have a boot parameter currently ("useapictimer") to switch back to original
> local APIC timer way of doing things.

I'm rather reluctant to advocate the broadcast scheme as i can see it
breaking on a lot of systems, e.g. SMP systems which use i8259 (as you
noted), IBM x440 and ES7000. If anything the default mode should be APIC
timer and have a parameter to disable it. Regarding things like variable
timer ticks, reprogramming the PIT is slow, and using it extensively for
such sounds like a step in the wrong direction. Is this feature/bug going
to proliferate amongst newer processor local APICs?


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