Hi Jason, Thanks for your reply! I am more concerned with polling mode about virtio-blk right now. Later I will focus on polling mode on virtio-net. I don't know whether the polling mode is already existed for virtio-blk or we should implement it by ourselves if we need this feature. Thanks for your time!
Best Wishes, Yaohui Hu On Sun, Sep 29, 2013 at 5:29 AM, Jason Wang <jasow...@redhat.com> wrote: > On 09/28/2013 02:56 AM, Hu Yaohui wrote: > > Hi All, > > I am wondering whether virtio has provided polling mode already. > > Instead of sending a event from guest to host through eventfd on guest > > side and inject an interrupt into guest on host side to notify each > > other? Could both sides keep polling the Vring to communicate with > > each other? > > Thanks for your time! > > > > For virtio-net, both qemu and driver (at least Linux) mix using polling > and notification. Usually one side will disable the notification from > another side when it gets an interrupt, and then enter the polling mode > until no more buffers submitted from another side. After this it will > enable the interrupts again. > > One of the method to improve this a little bit is to do the busy polling > even if there's no new buffers in case the other side will submit one or > more shortly. Linux has implemented this as low latency polling for > network stack (see http://lwn.net/Articles/551284/). It will do busy > polling for a time which can be configured by user. I've played a little > bit of this for both virtio-net and vhost, it can improves the latency > (more obvious for single session test) at the cost of extra cpu > overhead. The key to balance them is to choose time spent on busy > polling correctly. I don't think about it further but maybe we can make > it adaptive. > > Best Wishes, > > Yaohui > > >
