Messages in this thread | | | Subject | Re: [RFC v4 3/5] virtio_ring: add packed ring support | From | Jason Wang <> | Date | Thu, 17 May 2018 20:01:52 +0800 |
| |
On 2018年05月16日 22:33, Tiwei Bie wrote: > On Wed, May 16, 2018 at 10:05:44PM +0800, Jason Wang wrote: >> On 2018年05月16日 21:45, Tiwei Bie wrote: >>> On Wed, May 16, 2018 at 08:51:43PM +0800, Jason Wang wrote: >>>> On 2018年05月16日 20:39, Tiwei Bie wrote: >>>>> On Wed, May 16, 2018 at 07:50:16PM +0800, Jason Wang wrote: >>>>>> On 2018年05月16日 16:37, Tiwei Bie wrote: > [...] >>>>>>> +static void detach_buf_packed(struct vring_virtqueue *vq, unsigned int head, >>>>>>> + unsigned int id, void **ctx) >>>>>>> +{ >>>>>>> + struct vring_packed_desc *desc; >>>>>>> + unsigned int i, j; >>>>>>> + >>>>>>> + /* Clear data ptr. */ >>>>>>> + vq->desc_state[id].data = NULL; >>>>>>> + >>>>>>> + i = head; >>>>>>> + >>>>>>> + for (j = 0; j < vq->desc_state[id].num; j++) { >>>>>>> + desc = &vq->vring_packed.desc[i]; >>>>>>> + vring_unmap_one_packed(vq, desc); >>>>>> As mentioned in previous discussion, this probably won't work for the case >>>>>> of out of order completion since it depends on the information in the >>>>>> descriptor ring. We probably need to extend ctx to record such information. >>>>> Above code doesn't depend on the information in the descriptor >>>>> ring. The vq->desc_state[] is the extended ctx. >>>>> >>>>> Best regards, >>>>> Tiwei Bie >>>> Yes, but desc is a pointer to descriptor ring I think so >>>> vring_unmap_one_packed() still depends on the content of descriptor ring? >>>> >>> I got your point now. I think it makes sense to reserve >>> the bits of the addr field. Driver shouldn't try to get >>> addrs from the descriptors when cleanup the descriptors >>> no matter whether we support out-of-order or not. >> Maybe I was wrong, but I remember spec mentioned something like this. > You're right. Spec mentioned this. I was just repeating > the spec to emphasize that it does make sense. :) > >>> But combining it with the out-of-order support, it will >>> mean that the driver still needs to maintain a desc/ctx >>> list that is very similar to the desc ring in the split >>> ring. I'm not quite sure whether it's something we want. >>> If it is true, I'll do it. So do you think we also want >>> to maintain such a desc/ctx list for packed ring? >> To make it work for OOO backends I think we need something like this >> (hardware NIC drivers are usually have something like this). > Which hardware NIC drivers have this?
It's quite common I think, e.g driver track e.g dma addr and page frag somewhere. e.g the ring->rx_info in mlx4 driver.
Thanks
> >> Not for the patch, but it looks like having a OUT_OF_ORDER feature bit is >> much more simpler to be started with. > +1 > > Best regards, > Tiwei Bie
| |