From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:56993) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SmN2C-0004Wd-Ma for qemu-devel@nongnu.org; Wed, 04 Jul 2012 06:42:18 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1SmN2A-0005pG-Td for qemu-devel@nongnu.org; Wed, 04 Jul 2012 06:42:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:64821) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1SmN2A-0005pA-LR for qemu-devel@nongnu.org; Wed, 04 Jul 2012 06:42:10 -0400 Date: Wed, 4 Jul 2012 13:42:24 +0300 From: "Michael S. Tsirkin" Message-ID: <20120704104224.GA21704@redhat.com> References: <20120702091813.GF8268@redhat.com> <4FF16A21.7050309@siemens.com> <4FF16D54.3020801@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4FF16D54.3020801@redhat.com> Subject: Re: [Qemu-devel] plan for device assignment upstream List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Avi Kivity Cc: Jan Kiszka , Marcelo Tosatti , Michael Tokarev , "qemu-devel@nongnu.org" , kvm On Mon, Jul 02, 2012 at 12:43:48PM +0300, Avi Kivity wrote: > 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. This is more or less what I had in mind and what Anthony objects to. > -- > error compiling committee.c: too many arguments to function >