On Wed, Dec 19, 2012 at 04:53:22PM +0800, Asias He wrote: > 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. Okay great. I have one other last optimization up my sleeve, that should hopefully make it as fast as with the hack. > -- > Asias -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
