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Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path

From: Avi Kivity
Subject: Re: [Qemu-devel] [PATCH] pc: Clean up PIC-to-APIC IRQ path
Date: Sun, 04 Sep 2011 15:17:54 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0

On 08/31/2011 01:53 PM, Jan Kiszka wrote:
On 2011-08-31 10:25, Peter Maydell wrote:
>  On 30 August 2011 20:28, Jan Kiszka<address@hidden>  wrote:
>>  Yes, that's the current state. Once we have bidirectional IRQ links in
>>  place (pushing downward, querying upward - required to skip IRQ routers
>>  for fast, lockless deliveries), that should change again.
>  Can you elaborate a bit more on this? I don't think anybody has
>  proposed links with their own internal state before in the qdev/qom
>  discussions...

That basic idea is to allow

a) a discovery of the currently active IRQ path from source to sink
    (that would be possible via QOM just using forward links)

b) skip updating the states of IRQ routers in the common case, just
    signaling directly the sink from the source (to allow in-kernel IRQ
    delivery or to skip taking some device locks). Whenever some router
    is queried for its current IRQ line state, it would have to ask the
    preceding IRQ source for its state. So we need a backward link.

We haven't thought about how this could be implemented in details yet
though. Among other things, it heavily depends on the final QOM design.

Looks like a similar path to the memory API. A declarative description of the interrupt hierarchy allows routes to be precalculated and flattened.

(here it's strictly an optimization; with the memory API it's a requirement since kvm requires a flattened representation, and tcg is greatly simplified by it).

error compiling committee.c: too many arguments to function

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