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[Qemu-devel] Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback

From: Avi Kivity
Subject: [Qemu-devel] Re: [RFC PATCH 4/5] APIC/IOAPIC EOI callback
Date: Mon, 12 Jul 2010 09:33:12 +0300
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20100621 Fedora/3.0.5-1.fc13 Thunderbird/3.0.5

On 07/11/2010 09:30 PM, Avi Kivity wrote:
Registering an eventfd for the eoi seems like a reasonable alternative.

I'm worried about that racing (with what?)

I don't think there's a problem.

First, the EOI message is itself asynchronous. While the write to the local APIC is synchronous, effects on the rest of the system are effected using an APIC message, which travels asynchronously.

Second, a component that needs timely information doesn't have to wait; it can read the eventfd and be sure it has seen all EOIs up to now.

I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.

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