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. Thanks, Yongji
