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