From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: KVM in-kernel APIC update Date: Thu, 05 Apr 2007 09:48:59 +0300 Message-ID: <46149BDB.5040204@qumranet.com> References: <46128F80.BA47.005A.0@novell.com> <46135686.4090905@qumranet.com> <46138A98.BA47.005A.0@novell.com> <4613D736.1080207@qumranet.com> <4613959F.BA47.005A.0@novell.com> <4613E3CB.6000904@qumranet.com> <4613A090.BA47.005A.0@novell.com> <20070404202046.GD6070@elte.hu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: Ingo Molnar Return-path: In-reply-to: <20070404202046.GD6070-X9Un+BFzKDI@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Ingo Molnar wrote: > there is a remote possibility that some OSs depend on certain devices > being level-triggered: for example if you get an IRQ from a > level-triggered device and _dont_ deassert that signal from the IRQ > handler (intentionally so), then the semantics of current hardware will > cause a second interrupt to be sent by the PIC, after the APIC message > has been EOI-ed in the local APIC. While such "repeat interrupts" would > be pure madness to rely on i think, i'm not sure it's not being done. > Note that if the same IO-APIC pin is set up to detect edges then not > deasserting the signal would not cause a 'repeat interrupt'. Whether > such accurate emulation of signalling is needed depends on the hardware > semantics of the devices we emulate. > > Don't all OSes heavily depend on level-triggered interrupts for irq line sharing? -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV