Messages in this thread | | | Subject | Re: [RFC v4 3/5] virtio_ring: add packed ring support | From | Jason Wang <> | Date | Wed, 16 May 2018 22:05:44 +0800 |
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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: >>> [...] >>>>> struct vring_virtqueue { >>>>> @@ -116,6 +117,9 @@ struct vring_virtqueue { >>>>> /* Last written value to driver->flags in >>>>> * guest byte order. */ >>>>> u16 event_flags_shadow; >>>>> + >>>>> + /* ID allocation. */ >>>>> + struct idr buffer_id; >>>> I'm not sure idr is fit for the performance critical case here. Need to >>>> measure its performance impact, especially if we have few unused slots. >>> I'm also not sure.. But fortunately, it should be quite easy >>> to replace it with something else without changing other code. >>> If it will really hurt the performance, I'll change it. >> We may want to do some benchmarking/profiling to see. > Yeah! > >>>>> }; >>>>> }; >>> [...] >>>>> +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.
> > 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).
Not for the patch, but it looks like having a OUT_OF_ORDER feature bit is much more simpler to be started with.
Thanks
> > Best regards, > Tiwei Bie
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