From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [RFC] Deferred interrupt handling. Date: Wed, 18 Jul 2007 19:46:13 +0300 Message-ID: <469E43D5.70802@qumranet.com> References: <005901c7c921$79c006c0$6d401440$@com> <20070718123040.615795b7@the-village.bc.nu> <64F9B87B6B770947A9F8391472E032160CC16C92@ehost011-8.exch011.intermedia.net> <20070718174736.0baf6d0e@the-village.bc.nu> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Alan Cox Return-path: In-Reply-To: <20070718174736.0baf6d0e-v58gJUvfdfWUJIigds3554dd74u8MsAO@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 Alan Cox wrote: >> What if we will force the specific device to the end of the list. Once >> IRQ_NONE was returned by the other devices, we will mask the irq, >> forward the irq to the guest, issue a timer for 1msec. Motivation: >> 1msec is long enough for the guest to ack the irq + host unmask the irq >> > > It makes no difference. The deadlock isn't fixable by timing hacks. > Consider the following sequence > > > Guest0 - blocked on I/O > > IRQ14 from your hardware > Block IRQ14 > Sent to guest (guest is blocked) > > IRQ14 from hard disk > Ignored (as blocked) > > Deadlock > IMO the only reasonable solution is to disallow interrupt forwarding with shared irqs. If someone later comes up with a bright idea, we can implement it. Otherwise the problem will solve itself with hardware moving to msi. -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/