From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from [140.186.70.92] (port=44231 helo=eggs.gnu.org) by lists.gnu.org with esmtp (Exim 4.43) id 1PhSNQ-0001RM-4k for qemu-devel@nongnu.org; Mon, 24 Jan 2011 14:47:08 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1PhSN3-0006Yi-VC for qemu-devel@nongnu.org; Mon, 24 Jan 2011 14:46:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:37411) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1PhSN3-0006Yb-Lu for qemu-devel@nongnu.org; Mon, 24 Jan 2011 14:46:37 -0500 Message-ID: <4D3DD775.3060003@redhat.com> Date: Mon, 24 Jan 2011 20:48:05 +0100 From: Kevin Wolf MIME-Version: 1.0 Subject: Re: [Qemu-devel] [PATCH v5 2/4] virtio-pci: Use ioeventfd for virtqueue notify References: <1292166128-10874-1-git-send-email-stefanha@linux.vnet.ibm.com> <1292166128-10874-3-git-send-email-stefanha@linux.vnet.ibm.com> <4D3DCADC.6010308@redhat.com> <20110124193653.GC29941@redhat.com> In-Reply-To: <20110124193653.GC29941@redhat.com> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit List-Id: qemu-devel.nongnu.org List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Stefan Hajnoczi , qemu-devel@nongnu.org, Stefan Hajnoczi Am 24.01.2011 20:36, schrieb Michael S. Tsirkin: > On Mon, Jan 24, 2011 at 07:54:20PM +0100, Kevin Wolf wrote: >> Am 12.12.2010 16:02, schrieb Stefan Hajnoczi: >>> Virtqueue notify is currently handled synchronously in userspace virtio. This >>> prevents the vcpu from executing guest code while hardware emulation code >>> handles the notify. >>> >>> On systems that support KVM, the ioeventfd mechanism can be used to make >>> virtqueue notify a lightweight exit by deferring hardware emulation to the >>> iothread and allowing the VM to continue execution. This model is similar to >>> how vhost receives virtqueue notifies. >>> >>> The result of this change is improved performance for userspace virtio devices. >>> Virtio-blk throughput increases especially for multithreaded scenarios and >>> virtio-net transmit throughput increases substantially. >>> >>> Some virtio devices are known to have guest drivers which expect a notify to be >>> processed synchronously and spin waiting for completion. Only enable ioeventfd >>> for virtio-blk and virtio-net for now. >>> >>> Care must be taken not to interfere with vhost-net, which uses host >>> notifiers. If the set_host_notifier() API is used by a device >>> virtio-pci will disable virtio-ioeventfd and let the device deal with >>> host notifiers as it wishes. >>> >>> After migration and on VM change state (running/paused) virtio-ioeventfd >>> will enable/disable itself. >>> >>> * VIRTIO_CONFIG_S_DRIVER_OK -> enable virtio-ioeventfd >>> * !VIRTIO_CONFIG_S_DRIVER_OK -> disable virtio-ioeventfd >>> * virtio_pci_set_host_notifier() -> disable virtio-ioeventfd >>> * vm_change_state(running=0) -> disable virtio-ioeventfd >>> * vm_change_state(running=1) -> enable virtio-ioeventfd >>> >>> Signed-off-by: Stefan Hajnoczi >> >> On current git master I'm getting hangs when running iozone on a >> virtio-blk disk. "Hang" means that it's not responsive any more and has >> 100% CPU consumption. >> >> I bisected the problem to this patch. Any ideas? >> >> Kevin > > Does it help if you set ioeventfd=off on command line? Yes, with ioeventfd=off it seems to work fine. Kevin