From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:47703) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ewhAY-0005Fq-MR for qemu-devel@nongnu.org; Fri, 16 Mar 2018 00:40:43 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ewhAT-0000pd-NM for qemu-devel@nongnu.org; Fri, 16 Mar 2018 00:40:42 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54316 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ewhAT-0000pQ-IN for qemu-devel@nongnu.org; Fri, 16 Mar 2018 00:40:37 -0400 Date: Fri, 16 Mar 2018 12:40:17 +0800 From: Peter Xu Message-ID: <20180316044017.GC2477@xz-mi> References: <20180315212634.15150.88094.stgit@gimli.home> <20180315213157.15150.86812.stgit@gimli.home> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180315213157.15150.86812.stgit@gimli.home> Subject: Re: [Qemu-devel] [PATCH v2 3/3] vfio/pci: Add ioeventfd support List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alex Williamson Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, eric.auger@redhat.com, aik@ozlabs.ru On Thu, Mar 15, 2018 at 03:31:58PM -0600, Alex Williamson wrote: > The ioeventfd here is actually irqfd handling of an ioeventfd such as > supported in KVM. A user is able to pre-program a device write to > occur when the eventfd triggers. This is yet another instance of > eventfd-irqfd triggering between KVM and vfio. The impetus for this > is high frequency writes to pages which are virtualized in QEMU. > Enabling this near-direct write path for selected registers within > the virtualized page can improve performance and reduce overhead. > Specifically this is initially targeted at NVIDIA graphics cards where > the driver issues a write to an MMIO register within a virtualized > region in order to allow the MSI interrupt to re-trigger. > > Signed-off-by: Alex Williamson Reviewed-by: Peter Xu -- Peter Xu