From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:55205) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TlFMh-0005dS-6p for qemu-devel@nongnu.org; Wed, 19 Dec 2012 03:51:02 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1TlFMe-0000dY-JF for qemu-devel@nongnu.org; Wed, 19 Dec 2012 03:50:59 -0500 Received: from mx1.redhat.com ([209.132.183.28]:60951) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1TlFMe-0000dI-BW for qemu-devel@nongnu.org; Wed, 19 Dec 2012 03:50:56 -0500 Message-ID: <50D18082.50509@redhat.com> Date: Wed, 19 Dec 2012 16:53:22 +0800 From: Asias He MIME-Version: 1.0 References: In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH 0/3] virtio: don't poll masked vectors with irqfd List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: Jan Kiszka , Marcelo Tosatti , qemu-devel@nongnu.org, kvm@vger.kernel.org, Peter Maydell On 12/18/2012 08:39 PM, Michael S. Tsirkin wrote: > At the moment when vector is masked virtio will poll it > in userspace, even if it is handled by irqfd. > This is done in order to update pending bits, but > it's not really required until someone reads the pending bits. > On the other hand this read results in extra io thread wakeups. > > As we only implement the pending bits as a compatibility > feature (read - real drivers don't use it), we can defer > the irqfd poll until the read actually happens. > > This does not seem to affect vhost-net speed > in simple benchmarks but could help block: both > vhost-blk and dataplane when using irqfd, > and I also think this is cleaner than enabling/disabling > notifiers all the time. > > This will also be the basis for future optimizations. > > Michael S. Tsirkin (3): > msi: add API to get notified about pending bit poll > msix: expose access to masked/pending state > virtio-pci: don't poll masked vectors > > hw/pci/msix.c | 19 +++++++++++++++---- > hw/pci/msix.h | 6 +++++- > hw/pci/pci.h | 4 ++++ > hw/vfio_pci.c | 2 +- > hw/virtio-pci.c | 53 +++++++++++++++++++++++++++++++++++++++++------------ > 5 files changed, 66 insertions(+), 18 deletions(-) The performance boost is significant here. It is close to the result of dropping msix_fire_vector_notifier() hack. -- Asias