On Mon, Oct 16, 2023 at 8:01 PM Xuan Zhuo [off-list ref] wrote:

Not specific to this patch but any plan to fix the big mode?

+       size = virtqueue_get_vring_size(sq->vq);
+
+       size += MAX_SKB_FRAGS + 2;
+
+       sq->dmainfo.head = kcalloc(size, sizeof(*sq->dmainfo.head), GFP_KERNEL);
+       if (!sq->dmainfo.head)
+               return -ENOMEM;
+
+       err = virtqueue_set_dma_premapped(sq->vq);
+       if (err) {
+               kfree(sq->dmainfo.head);
+               return err;
+       }
+
+       sq->dmainfo.free = NULL;
+
+       sq->do_dma = true;
+
+       for (i = 0; i < size; ++i) {
+               d = &sq->dmainfo.head[i];
+
+               d->next = sq->dmainfo.free;
+               sq->dmainfo.free = d;
+       }
+
+       return 0;
+}
+
+static void virtnet_set_premapped(struct virtnet_info *vi)
+{
+       int i;

        for (i = 0; i < vi->max_queue_pairs; i++) {
-               if (virtqueue_set_dma_premapped(vi->rq[i].vq))
+               if (!virtnet_sq_set_premapped(&vi->sq[i]))
+                       vi->sq[i].do_dma = true;
+
+               /* disable for big mode */
+               if (!vi->mergeable_rx_bufs && vi->big_packets)
                        continue;

-               vi->rq[i].do_dma = true;
+               if (!virtqueue_set_dma_premapped(vi->rq[i].vq))
+                       vi->rq[i].do_dma = true;
+       }
+}
+
+static struct virtnet_sq_dma *virtnet_sq_map_sg(struct virtnet_sq *sq, int nents, void *data)
+{
+       struct virtnet_sq_dma *d, *head;
+       struct scatterlist *sg;
+       int i;
+
+       head = NULL;
+
+       for_each_sg(sq->sg, sg, nents, i) {
+               sg->dma_address = virtqueue_dma_map_single_attrs(sq->vq, sg_virt(sg),
+                                                                sg->length,
+                                                                DMA_TO_DEVICE, 0);
+               if (virtqueue_dma_mapping_error(sq->vq, sg->dma_address))
+                       goto err;
+
+               d = sq->dmainfo.free;
+               sq->dmainfo.free = d->next;
+
+               d->addr = sg->dma_address;
+               d->len = sg->length;
+
+               d->next = head;
+               head = d;

It's really a pity that we need to duplicate those DMA metata twice.
Could we invent a new API to just fetch it from the virtio core?

+       }
+
+       head->data = data;
+
+       return (void *)((unsigned long)head | ((unsigned long)data & VIRTIO_XMIT_DATA_MASK));

If we packed everything into dmainfo, we can leave the type (XDP vs
skb) there to avoid trick like packing it into the pointer here?

Thanks