From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: plan for device assignment upstream Date: Mon, 02 Jul 2012 12:43:48 +0300 Message-ID: <4FF16D54.3020801@redhat.com> References: <20120702091813.GF8268@redhat.com> <4FF16A21.7050309@siemens.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Michael S. Tsirkin" , Marcelo Tosatti , kvm , Michael Tokarev , "qemu-devel@nongnu.org" To: Jan Kiszka Return-path: Received: from mx1.redhat.com ([209.132.183.28]:51928 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932717Ab2GBJn4 (ORCPT ); Mon, 2 Jul 2012 05:43:56 -0400 In-Reply-To: <4FF16A21.7050309@siemens.com> Sender: kvm-owner@vger.kernel.org List-ID: On 07/02/2012 12:30 PM, Jan Kiszka wrote: > On 2012-07-02 11:18, Michael S. Tsirkin wrote: >> I've been thinking hard about Jan's patches for device >> assignment. Basically while I thought it makes sense >> to make all devices: assignment and not - behave the >> same and use same APIs for injecting irqs, Anthony thinks there is huge >> value in making irq propagation hierarchical and device assignment >> should be special cased. > > On the long term, we will need direct injection, ie. caching, to allow > making it lock-less. Stepping through all intermediate layers will cause > troubles, at least performance-wise, when having to take and drop a lock > at each stop. So we precalculate everything beforehand. Instead of each qemu_irq triggering a callback, calculating the next hop and firing the next qemu_irq, configure each qemu_irq array with a function that describes how to take the next hop. Whenever the configuration changes, recalculate all routes. For device assignment or vhost, we can have a qemu_irq_irqfd() which converts a qemu_irq to an eventfd. If the route calculations determine that it can be serviced via a real irqfd, they also configure it as an irqfd. Otherwise qemu configures a poll on this eventfd and calls the callback when needed. -- error compiling committee.c: too many arguments to function