On Fri, Mar 5, 2021 at 3:01 PM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > On 2021/3/5 2:36 下午, Yongji Xie wrote: > > On Fri, Mar 5, 2021 at 11:42 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > >> > >> On 2021/3/5 11:30 上午, Yongji Xie wrote: > >>> On Fri, Mar 5, 2021 at 11:05 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > >>>> On 2021/3/4 4:58 下午, Yongji Xie wrote: > >>>>> On Thu, Mar 4, 2021 at 2:59 PM Jason Wang <jasowang@xxxxxxxxxx> wrote: > >>>>>> On 2021/2/23 7:50 下午, Xie Yongji wrote: > >>>>>>> This patch introduces a workqueue to support injecting > >>>>>>> virtqueue's interrupt asynchronously. This is mainly > >>>>>>> for performance considerations which makes sure the push() > >>>>>>> and pop() for used vring can be asynchronous. > >>>>>> Do you have pref numbers for this patch? > >>>>>> > >>>>> No, I can do some tests for it if needed. > >>>>> > >>>>> Another problem is the VIRTIO_RING_F_EVENT_IDX feature will be useless > >>>>> if we call irq callback in ioctl context. Something like: > >>>>> > >>>>> virtqueue_push(); > >>>>> virtio_notify(); > >>>>> ioctl() > >>>>> ------------------------------------------------- > >>>>> irq_cb() > >>>>> virtqueue_get_buf() > >>>>> > >>>>> The used vring is always empty each time we call virtqueue_push() in > >>>>> userspace. Not sure if it is what we expected. > >>>> I'm not sure I get the issue. > >>>> > >>>> THe used ring should be filled by virtqueue_push() which is done by > >>>> userspace before? > >>>> > >>> After userspace call virtqueue_push(), it always call virtio_notify() > >>> immediately. In traditional VM (vhost-vdpa) cases, virtio_notify() > >>> will inject an irq to VM and return, then vcpu thread will call > >>> interrupt handler. But in container (virtio-vdpa) cases, > >>> virtio_notify() will call interrupt handler directly. So it looks like > >>> we have to optimize the virtio-vdpa cases. But one problem is we don't > >>> know whether we are in the VM user case or container user case. > >> > >> Yes, but I still don't get why used ring is empty after the ioctl()? > >> Used ring does not use bounce page so it should be visible to the kernel > >> driver. What did I miss :) ? > >> > > Sorry, I'm not saying the kernel can't see the correct used vring. I > > mean the kernel will consume the used vring in the ioctl context > > directly in the virtio-vdpa case. In userspace's view, that means > > virtqueue_push() is used vring's producer and virtio_notify() is used > > vring's consumer. They will be called one by one in one thread rather > > than different threads, which looks odd and has a bad effect on > > performance. > > > Yes, that's why we need a workqueue (WQ_UNBOUND you used). Or do you > want to squash this patch into patch 8? > > So I think we can see obvious difference when virtio-vdpa is used. > But it looks like we don't need this workqueue in vhost-vdpa cases. Any suggestions? Thanks, Yongji
