Re: [Xen-devel] [PATCH] make HVM PIC emulation code SMP-safe

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 17 May 2006, at 07:01, Dong, Eddie wrote:

>     In either way, when Xen detects the guest has disabled PIC, the 
> PIC IRQ generation logic can be removed for both performance and 
> simplicity. So even VP0 doesn't need to get/queue interrupt from PIC. 
> The ideal solution may be that we need to define some registable APIs 
> in HVM virtual weired interrupt controller logic. At startup time, we 
> regieter PIC APIs, and later on replace it with APIC's (the transition 
> time need special concern while it is non performance critical path).
Don;t some OSes (e.g., older Linux) expect to be able to keep some 
interrupts routed through 8259 and then have the output of that plumbed 
to an IOAPIC pin? Or can they always fall back from that (is there real 
hardware that isn't able to route 8259 via an IOAPIC)?
 -- Keir

>     Anyway, 2) PIC I/O access may need to be SMP safe (maybe a big 
> lock for simplicity), 3) IOAPIC needs to be SMP safe. Then we try to 
> keep minimal changes to device models with that in Qemu (yes we 
> already have some) for future maintain effort. You are very welcome 
> here.
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