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

[Zwane Mwaikambo <zwane@arm.linux.org.uk>]

On Fri, 29 Apr 2005, Venkatesh Pallipadi wrote:

> 
> Background: 
> Local APIC timer stops functioning when CPU is in C3 state. As a
> result the local APIC timer interrupt will fire at uncertain times, depending
> on how long we spend in C3 state. And this has two side effects
> * Idle balancing will not happen as we expect it to.
> * Kernel statistics for idle time will not be proper (as we get less LAPIC
>   interrupts when we are idle). This can result in confusing other parts of
>   kernel (like ondemand cpufreq governor) which depends on this idle stats.
> 
> 
> 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.

This all looks like it'll contend on irq0 related locks really badly, have 
you profiled this?

Thanks,
	Zwane

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