From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43696) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlwD3-0000UF-6E for qemu-devel@nongnu.org; Wed, 05 Nov 2014 03:45:03 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1XlwCx-0006QY-4H for qemu-devel@nongnu.org; Wed, 05 Nov 2014 03:44:57 -0500 Received: from mail-wi0-f169.google.com ([209.85.212.169]:40068) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1XlwCw-0006QO-Tr for qemu-devel@nongnu.org; Wed, 05 Nov 2014 03:44:51 -0500 Received: by mail-wi0-f169.google.com with SMTP id n3so10745202wiv.0 for ; Wed, 05 Nov 2014 00:44:49 -0800 (PST) Message-ID: <5459E343.6030907@linaro.org> Date: Wed, 05 Nov 2014 09:43:47 +0100 From: Eric Auger MIME-Version: 1.0 References: <1414225494-2208-1-git-send-email-john.liuli@huawei.com> <544E2B18.8010702@huawei.com> In-Reply-To: <544E2B18.8010702@huawei.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [RFC PATCH 0/2] virtio-mmio: add irqfd support for vhost-net based on virtio-mmio List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Li Liu , Peter Maydell Cc: Joel Schopp , "eric.auger@st.com" , Yingshiuan Pan , "Michael S. Tsirkin" , remy.gauguey@cea.fr, Rusty Russell , lkml - Kernel Mailing List , Nikolay Nikolaev , QEMU Developers , peter.huangpeng@huawei.com, "virtualization@lists.linux-foundation.org" , Christoffer Dall On 10/27/2014 12:23 PM, Li Liu wrote: > > > On 2014/10/27 17:37, Peter Maydell wrote: >> On 25 October 2014 09:24, john.liuli wrote: >>> To get the interrupt reason to support such VIRTIO_NET_F_STATUS >>> features I add a new register offset VIRTIO_MMIO_ISRMEM which >>> will help to establish a shared memory region between qemu and >>> virtio-mmio device. Then the interrupt reason can be accessed by >>> guest driver through this region. At the same time, the virtio-mmio >>> dirver check this region to see irqfd is supported or not during >>> the irq handler registration, and different handler will be assigned. >> >> If you want to add a new register you should probably propose >> an update to the virtio spec. However, it seems to me it would >> be better to get generic PCI/PCIe working on the ARM virt >> board instead; then we can let virtio-mmio quietly fade away. >> This has been on the todo list for ages (and there have been >> RFC patches posted for plain PCI), it's just nobody's had time >> to work on it. >> >> thanks >> -- PMM >> > > So you mean virtio-mmio will be replaced by PCI/PCIe on ARM at last? > If so, let this patch go with the wind:). Thx. Hi, As a fix of current situation where ISR is only partially updated when vhost-irqfd handles standard IRQ and waiting for PCI emuluation, wouldn't it make sense to store ISR content on vhost driver side and introduce ioctls to read/write it. When using vhost BE, virtio QEMU device would use those ioctl to read/update the ISR content. On top of that we would update the ISR in vhost before triggering the irqfd. If I do not miss anything this would at least make things functional with irqfd. As a second step, we could try to introduce in-kernel emulation of ISR/ACK to fix the performance issue related to going to user-side each time ISR/ACK accesses are done. Do you think it is worth investigating this direction? Thank you in advance Best Regards Eric > > Li. >> . >> > >