On Mon, Mar 8, 2021 at 11:04 AM Jason Wang <jasowang@xxxxxxxxxx> wrote: > > > On 2021/3/5 4:12 下午, Yongji Xie wrote: > > On Fri, Mar 5, 2021 at 3:37 PM Jason Wang <jasowang@xxxxxxxxxx> wrote: > >> > >> On 2021/3/5 3:27 下午, Yongji Xie wrote: > >>> 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? > >> > >> I haven't had a deep thought. But I feel we can solve this by using the > >> irq bypass manager (or something similar). Then we don't need it to be > >> relayed via workqueue and vdpa. But I'm not sure how hard it will be. > >> > > Or let vdpa bus drivers give us some information? > > > This kind of 'type' is proposed in the early RFC of vDPA series. One > issue is that at device level, we should not differ virtio from vhost, > so if we introduce that, it might encourge people to design a device > that is dedicated to vhost or virtio which might not be good. > > But we can re-visit this when necessary. > OK, I see. How about adding some information in ops.set_vq_cb()? Thanks, Yongji
