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    SubjectRe: [patch] genapic: optimize & fix APIC mode setup
    Date
    On Saturday 11 November 2006 16:14, Ingo Molnar wrote:
    > From: Ingo Molnar <mingo@elte.hu>
    >
    > this patch fixes a couple of inconsistencies/problems i found while
    > reviewing the x86_64 genapic code (when i was chasing mysterious eth0
    > timeouts that would only trigger if CPU_HOTPLUG is enabled):
    >
    > - AMD systems defaulted to the slower flat-physical mode instead
    > of the flat-logical mode. The only restriction on AMD systems
    > is that they should not use clustered APIC mode.

    This will open a race on CPU hotunplug unfortunately
    (common for multi core suspend)

    >
    > - removed the CPU hotplug hacks, switching the default for small
    > systems back from phys-flat to logical-flat. The switching to logical
    > flat mode on small systems fixed sporadic ethernet driver timeouts i
    > was getting on a dual-core Athlon64 system:

    That will break CPU hotplug on some Intel systems (Ashok can give details)

    That is caused ethernet timeouts is weird, probably needs to be root caused.

    > NETDEV WATCHDOG: eth0: transmit timed out
    > eth0: Transmit timeout, status 0c 0005 c07f media 80.
    > eth0: Tx queue start entry 32 dirty entry 28.
    > eth0: Tx descriptor 0 is 0008a04a. (queue head)
    > eth0: Tx descriptor 1 is 0008a04a.
    > eth0: Tx descriptor 2 is 0008a04a.
    > eth0: Tx descriptor 3 is 0008a04a.
    > eth0: link up, 100Mbps, full-duplex, lpa 0xC5E1
    >
    > - The use of '<= 8' was a bug by itself (the valid APIC ids
    > for logical flat mode go from 0 to 7, not 0 to 8). The new logic
    > is to use logical flat mode on both AMD and Intel systems, and
    > to only switch to physical mode when logical mode cannot be used.
    > If CPU hotplug is racy wrt. APIC shutdown then CPU hotplug needs
    > fixing, not the whole IRQ system be made inconsistent and slowed
    > down.

    Yes that needs to be fixed.

    -Andi
    -
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