Re: [RFC PATCH 0/6] kvm/ppc/mpic: in-kernel irqchip

Scott Wood
2013-02-18T23:05:59Z

On 02/18/2013 06:04:51 AM, Gleb Natapov wrote:
> Can you tell us why mpic should be in kernel? Is it used often by
> modern
> guests or may be they prefer MSI for interrupt delivery (hmm may be
> MSIs
> are delivered through mpic too)?

Yes, MSIs are delivered through the mpic.

Plus, MSIs are only (normally) for PCI(e). We have embedded "system on
a chip"s with important non-PCI devices, which cannot use MSIs.

> On x86 we actually would've preferred
> to move PIC/IOAPIC form the kernel and leave only LAPIC there (but for
> historical reasons creation of PIC/IOAPIC/LAPIC are bundled together)
> hence my question.

We don't have that same split on this hardware. MPIC is one device
that covers all of it. Some of the functionality is per-CPU, but it is
not easily extracted from the rest.

-Scott