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SubjectRe: [patch] genapic: optimize & fix APIC mode setup
On Saturday 11 November 2006 16:14, Ingo Molnar wrote:
> From: Ingo Molnar <>
> 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.

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