From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Wood Subject: Re: [RFC PATCH 0/6] kvm/ppc/mpic: in-kernel irqchip Date: Mon, 18 Feb 2013 17:05:59 -0600 Message-ID: <1361228759.25178.3@snotra> References: <20130218120451.GB9817@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; delsp=Yes; format=Flowed Content-Transfer-Encoding: 8BIT Cc: Alexander Graf , , To: Gleb Natapov Return-path: In-Reply-To: <20130218120451.GB9817@redhat.com> (from gleb@redhat.com on Mon Feb 18 06:04:51 2013) Content-Disposition: inline Sender: kvm-ppc-owner@vger.kernel.org List-Id: kvm.vger.kernel.org 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