From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH] IRQ: manually EOI migrating line interrupts Date: Tue, 30 Aug 2011 16:19:24 +0100 Message-ID: <4E5CFF7C.90309@citrix.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Keir Fraser Cc: "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 30/08/11 15:38, Keir Fraser wrote: > On 30/08/2011 15:28, "Andrew Cooper" wrote: > >>> @@ -1739,6 +1739,14 @@ static void end_level_ioapic_irq (unsign >>> */ >>> i = IO_APIC_VECTOR(irq); >>> >>> + /* Manually EOI the old vector if we are moving to the new */ >>> + if ( vector && i != vector ) >>> + { >>> + int ioapic; >>> + for (ioapic = 0; ioapic < nr_ioapics; ioapic++) >>> + io_apic_eoi(ioapic, i); >>> + } >>> + > I don't know whether it's worth the effort, but we ought to be able to do > better than this and send EOI to exactly the correct IO-APIC. I think > irq=gsi here? And we should know the gsi_base of every IO-APIC, so we can > work out in fact which pin of which IO-APIC needs clobbering? > > -- Keir irq does (or really should) equal gsi. I had not noticed gsi_base and gsi_end when making this fix. io_apic_eoi does not require a pin, but it is using IO-APIC registers which I can not find references to. The Local APIC document implies that you just write the vector to the EOI register, and the IO-APIC will work out which pin to clear. However, because Xen currently might assign the same vector to two pins in the same IO-APIC, changing the code at this point will not fix the problem - just make it rarer. Therefore, I would suggest that it is not worth the effort, as the problem is already very rare, and unlikely to be a problem with any sane hardware which avoids PCI INTx interrupts where possible. P.S. If anyone knows which manual contains the specificaion/programming guide for the IO-APIC, I would be very gratefull. Google always points to 82093AA datasheet which is very out of date. -- Andrew Cooper - Dom0 Kernel Engineer, Citrix XenServer T: +44 (0)1223 225 900, http://www.citrix.com