Messages in this thread | | | Subject | Re: [PATCH RFC 2/2] virtio_ring: support packed ring | From | Jason Wang <> | Date | Fri, 16 Mar 2018 16:34:28 +0800 |
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On 2018年03月16日 15:40, Tiwei Bie wrote: > On Fri, Mar 16, 2018 at 02:44:12PM +0800, Jason Wang wrote: >> On 2018年03月16日 14:10, Tiwei Bie wrote: >>> On Fri, Mar 16, 2018 at 12:03:25PM +0800, Jason Wang wrote: >>>> On 2018年02月23日 19:18, Tiwei Bie wrote: >>>>> Signed-off-by: Tiwei Bie <tiwei.bie@intel.com> >>>>> --- >>>>> drivers/virtio/virtio_ring.c | 699 +++++++++++++++++++++++++++++++++++++------ >>>>> include/linux/virtio_ring.h | 8 +- >>>>> 2 files changed, 618 insertions(+), 89 deletions(-) > [...] >>>>> cpu_addr, size, direction); >>>>> } >>>>> -static void vring_unmap_one(const struct vring_virtqueue *vq, >>>>> - struct vring_desc *desc) >>>>> +static void vring_unmap_one(const struct vring_virtqueue *vq, void *_desc) >>>>> { >>>> Let's split the helpers to packed/split version like other helpers? >>>> (Consider the caller has already known the type of vq). >>> Okay. >>> >> [...] >> >>>>> + desc[i].flags = flags; >>>>> + >>>>> + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); >>>>> + desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length); >>>>> + desc[i].id = cpu_to_virtio32(_vq->vdev, head); >>>> If it's a part of chain, we only need to do this for last buffer I think. >>> I'm not sure I've got your point about the "last buffer". >>> But, yes, id just needs to be set for the last desc. >> Right, I think I meant "last descriptor" :) >> >>>>> + prev = i; >>>>> + i++; >>>> It looks to me prev is always i - 1? >>> No. prev will be (vq->vring_packed.num - 1) when i becomes 0. >> Right, so prev = i ? i - 1 : vq->vring_packed.num - 1. > Yes, i wraps together with vq->wrap_counter in following code: > >>>>> + if (!indirect && i >= vq->vring_packed.num) { >>>>> + i = 0; >>>>> + vq->wrap_counter ^= 1; >>>>> + } > >>>>> + } >>>>> + } >>>>> + for (; n < (out_sgs + in_sgs); n++) { >>>>> + for (sg = sgs[n]; sg; sg = sg_next(sg)) { >>>>> + dma_addr_t addr = vring_map_one_sg(vq, sg, DMA_FROM_DEVICE); >>>>> + if (vring_mapping_error(vq, addr)) >>>>> + goto unmap_release; >>>>> + >>>>> + flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_NEXT | >>>>> + VRING_DESC_F_WRITE | >>>>> + VRING_DESC_F_AVAIL(vq->wrap_counter) | >>>>> + VRING_DESC_F_USED(!vq->wrap_counter)); >>>>> + if (!indirect && i == head) >>>>> + head_flags = flags; >>>>> + else >>>>> + desc[i].flags = flags; >>>>> + >>>>> + desc[i].addr = cpu_to_virtio64(_vq->vdev, addr); >>>>> + desc[i].len = cpu_to_virtio32(_vq->vdev, sg->length); >>>>> + desc[i].id = cpu_to_virtio32(_vq->vdev, head); >>>>> + prev = i; >>>>> + i++; >>>>> + if (!indirect && i >= vq->vring_packed.num) { >>>>> + i = 0; >>>>> + vq->wrap_counter ^= 1; >>>>> + } >>>>> + } >>>>> + } >>>>> + /* Last one doesn't continue. */ >>>>> + if (!indirect && (head + 1) % vq->vring_packed.num == i) >>>>> + head_flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); >>>> I can't get the why we need this here. >>> If only one desc is used, we will need to clear the >>> VRING_DESC_F_NEXT flag from the head_flags. >> Yes, I meant why following desc[prev].flags won't work for this? > Because the update of desc[head].flags (in above case, > prev == head) has been delayed. The flags is saved in > head_flags.
Ok, but let's try to avoid modular here e.g tracking the number of sgs in a counter.
And I see lots of duplication in the above two loops, I believe we can unify them with a a single loop. the only difference is dma direction and write flag.
> >>>>> + else >>>>> + desc[prev].flags &= cpu_to_virtio16(_vq->vdev, ~VRING_DESC_F_NEXT); >>>>> + >>>>> + if (indirect) { >>>>> + /* FIXME: to be implemented */ >>>>> + >>>>> + /* Now that the indirect table is filled in, map it. */ >>>>> + dma_addr_t addr = vring_map_single( >>>>> + vq, desc, total_sg * sizeof(struct vring_packed_desc), >>>>> + DMA_TO_DEVICE); >>>>> + if (vring_mapping_error(vq, addr)) >>>>> + goto unmap_release; >>>>> + >>>>> + head_flags = cpu_to_virtio16(_vq->vdev, VRING_DESC_F_INDIRECT | >>>>> + VRING_DESC_F_AVAIL(wrap_counter) | >>>>> + VRING_DESC_F_USED(!wrap_counter)); >>>>> + vq->vring_packed.desc[head].addr = cpu_to_virtio64(_vq->vdev, addr); >>>>> + vq->vring_packed.desc[head].len = cpu_to_virtio32(_vq->vdev, >>>>> + total_sg * sizeof(struct vring_packed_desc)); >>>>> + vq->vring_packed.desc[head].id = cpu_to_virtio32(_vq->vdev, head); >>>>> + } >>>>> + >>>>> + /* We're using some buffers from the free list. */ >>>>> + vq->vq.num_free -= descs_used; >>>>> + >>>>> + /* Update free pointer */ >>>>> + if (indirect) { >>>>> + n = head + 1; >>>>> + if (n >= vq->vring_packed.num) { >>>>> + n = 0; >>>>> + vq->wrap_counter ^= 1; >>>>> + } >>>>> + vq->free_head = n; >>>> detach_buf_packed() does not even touch free_head here, so need to explain >>>> its meaning for packed ring. >>> Above code is for indirect support which isn't really >>> implemented in this patch yet. >>> >>> For your question, free_head stores the index of the >>> next avail desc. I'll add a comment for it or move it >>> to union and give it a better name in next version. >> Yes, something like avail_idx might be better. >> >>>>> + } else >>>>> + vq->free_head = i; >>>> ID is only valid in the last descriptor in the list, so head + 1 should be >>>> ok too? >>> I don't really get your point. The vq->free_head stores >>> the index of the next avail desc. >> I think I get your idea now, free_head has two meanings: >> >> - next avail index >> - buffer id > In my design, free_head is just the index of the next > avail desc. > > Driver can set anything to buffer ID.
Then you need another method to track id to context e.g hashing.
> And in my design, > I save desc index in buffer ID. > > I'll add comments for them. > >> If I'm correct, let's better add a comment for this. >> >>>>> + >>>>> + /* Store token and indirect buffer state. */ >>>>> + vq->desc_state[head].num = descs_used; >>>>> + vq->desc_state[head].data = data; >>>>> + if (indirect) >>>>> + vq->desc_state[head].indir_desc = desc; >>>>> + else >>>>> + vq->desc_state[head].indir_desc = ctx; >>>>> + >>>>> + virtio_wmb(vq->weak_barriers); >>>> Let's add a comment to explain the barrier here. >>> Okay. >>> >>>>> + vq->vring_packed.desc[head].flags = head_flags; >>>>> + vq->num_added++; >>>>> + >>>>> + pr_debug("Added buffer head %i to %p\n", head, vq); >>>>> + END_USE(vq); >>>>> + >>>>> + return 0; >>>>> + >>>>> +unmap_release: >>>>> + err_idx = i; >>>>> + i = head; >>>>> + >>>>> + for (n = 0; n < total_sg; n++) { >>>>> + if (i == err_idx) >>>>> + break; >>>>> + vring_unmap_one(vq, &desc[i]); >>>>> + i++; >>>>> + if (!indirect && i >= vq->vring_packed.num) >>>>> + i = 0; >>>>> + } >>>>> + >>>>> + vq->wrap_counter = wrap_counter; >>>>> + >>>>> + if (indirect) >>>>> + kfree(desc); >>>>> + >>>>> + END_USE(vq); >>>>> + return -EIO; >>>>> +} > [...] >>>>> @@ -1096,17 +1599,21 @@ struct virtqueue *vring_create_virtqueue( >>>>> if (!queue) { >>>>> /* Try to get a single page. You are my only hope! */ >>>>> - queue = vring_alloc_queue(vdev, vring_size(num, vring_align), >>>>> + queue = vring_alloc_queue(vdev, __vring_size(num, vring_align, >>>>> + packed), >>>>> &dma_addr, GFP_KERNEL|__GFP_ZERO); >>>>> } >>>>> if (!queue) >>>>> return NULL; >>>>> - queue_size_in_bytes = vring_size(num, vring_align); >>>>> - vring_init(&vring, num, queue, vring_align); >>>>> + queue_size_in_bytes = __vring_size(num, vring_align, packed); >>>>> + if (packed) >>>>> + vring_packed_init(&vring.vring_packed, num, queue, vring_align); >>>>> + else >>>>> + vring_init(&vring.vring_split, num, queue, vring_align); >>>> Let's rename vring_init to vring_init_split() like other helpers? >>> The vring_init() is a public API in include/uapi/linux/virtio_ring.h. >>> I don't think we can rename it. >> I see, then this need more thoughts to unify the API. > My thought is to keep the old API as is, and introduce > new types and helpers for packed ring.
I admit it's not a fault of this patch. But we'd better think of this in the future, consider we may have new kinds of ring.
> > More details can be found in this patch: > https://lkml.org/lkml/2018/2/23/243 > (PS. The type which has bit fields is just for reference, > and will be changed in next version.) > > Do you have any other suggestions?
No.
Thanks
> > Best regards, > Tiwei Bie > >>>>> - vq = __vring_new_virtqueue(index, vring, vdev, weak_barriers, context, >>>>> - notify, callback, name); >>>>> + vq = __vring_new_virtqueue(index, vring, packed, vdev, weak_barriers, >>>>> + context, notify, callback, name); >>>>> if (!vq) { >>>>> vring_free_queue(vdev, queue_size_in_bytes, queue, >>>>> dma_addr); > [...]
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