From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:47611) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S8UAY-0002ys-MQ for qemu-devel@nongnu.org; Fri, 16 Mar 2012 06:14:21 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S8U9x-0001nA-3h for qemu-devel@nongnu.org; Fri, 16 Mar 2012 06:13:58 -0400 Received: from thoth.sbs.de ([192.35.17.2]:31147) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S8U9w-0001mm-QH for qemu-devel@nongnu.org; Fri, 16 Mar 2012 06:13:21 -0400 Message-ID: <4F631232.8020904@siemens.com> Date: Fri, 16 Mar 2012 11:13:06 +0100 From: Jan Kiszka MIME-Version: 1.0 References: <4F61C2C5.6060700@cn.fujitsu.com> <4F62A7AF.9020706@cn.fujitsu.com> <4F62F97C.5080805@siemens.com> <4F62FC0C.9030302@cn.fujitsu.com> In-Reply-To: <4F62FC0C.9030302@cn.fujitsu.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] pci-assign can not work List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wen Congyang Cc: qemu-devel , kvm list , Markus Armbruster On 2012-03-16 09:38, Wen Congyang wrote: > At 03/16/2012 04:27 PM, Jan Kiszka Wrote: >> On 2012-03-16 03:38, Wen Congyang wrote: >>> At 03/15/2012 06:21 PM, Wen Congyang Wrote: >>>> Hi all >>>> >>>> When I use pci-assign, I meet the following error: >>>> >>>> Failed to assign irq for "hostdev0": Input/output error >>>> Perhaps you are assigning a device that shares an IRQ with another device? >>>> >>>> Is it a bug or I miss something? >>> >>> Hi, Jan >>> >>> This problem is caused by your patch: >>> commit 6919115a8715c34cd80baa08422d90496f11f5d7 >>> Author: Jan Kiszka >>> Date: Thu Mar 8 11:10:27 2012 +0100 >>> >>> pci_assign: Flip defaults of prefer_msi and share_intx >>> >>> INTx sharing is a bit more expensive than exclusive host interrupts, but >>> this channel is not supposed to be used for high-performance scenarios >>> anyway. Modern devices support MSI/MSI-X and do not depend on using INTx >>> under critical workload, real old devices do not support INTx sharing >>> anyway. >>> >>> For those in the middle, the user experience is much better if they just >>> work even when IRQ sharing is required. If there is nothing to share, >>> share_intx=off can still be applied as tuning parameter. >>> >>> With INTx sharing as default, the primary reason for prefer_msi=on is >>> gone. Make it default off, specifically as it is known to cause troubles >>> with devices that have incomplete/broken MSI support or otherwise >>> stumble if host IRQ configuration does not match guest driver >>> expectation. >>> >>> Acked-by: Alex Williamson >>> Signed-off-by: Jan Kiszka >>> Signed-off-by: Marcelo Tosatti >>> >>> If I revert this commit. qemu can work. >>> >> >> This should be "solvable" by passing prefer_msi=on to the pci-assign >> device, or likely by updating your host kernel to latest kvm.git (to >> enable INTx sharing). > > Is there some way to find out if the kernel supports to enable INTx > sharing? QEMU does a feature check, but as a user you simply have to know which kernel version includes it (will be 3.4 or 3.5). Of course, that's not really handy. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux