On Mon, Jul 10, 2023 at 8:41 PM Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, 10 Jul 2023 07:59:03 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > On Mon, Jul 10, 2023 at 06:18:30PM +0800, Xuan Zhuo wrote:
> > > On Mon, 10 Jul 2023 05:40:21 -0400, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote:
> > > > On Mon, Jul 10, 2023 at 11:42:37AM +0800, Xuan Zhuo wrote:
> > > > > Currently, the virtio core will perform a dma operation for each
> > > > > operation. Although, the same page may be operated multiple times.
> > > > >
> > > > > The driver does the dma operation and manages the dma address based the
> > > > > feature premapped of virtio core.
> > > > >
> > > > > This way, we can perform only one dma operation for the same page. In
> > > > > the case of mtu 1500, this can reduce a lot of dma operations.
> > > > >
> > > > > Tested on Aliyun g7.4large machine, in the case of a cpu 100%, pps
> > > > > increased from 1893766 to 1901105. An increase of 0.4%.
> > > >
> > > > what kind of dma was there? an IOMMU? which vendors? in which mode
> > > > of operation?
> > >
> > >
> > > Do you mean this:
> > >
> > > [ 0.470816] iommu: Default domain type: Passthrough
> > >
> >
> > With passthrough, dma API is just some indirect function calls, they do
> > not affect the performance a lot.
>
>
> Yes, this benefit is worthless. I seem to have done a meaningless thing. The
> overhead of DMA I observed is indeed not too high.
Have you measured with iommu=strict?
Thanks
>
> Thanks.
>
>
> >
> > Try e.g. bounce buffer. Which is where you will see a problem: your
> > patches won't work.
> >
> >
> > > >
> > > > > Signed-off-by: Xuan Zhuo <xuanzhuo@xxxxxxxxxxxxxxxxx>
> > > >
> > > > This kind of difference is likely in the noise.
> > >
> > > It's really not high, but this is because the proportion of DMA under perf top
> > > is not high. Probably that much.
> >
> > So maybe not worth the complexity.
> >
> > > >
> > > >
> > > > > ---
> > > > > drivers/net/virtio_net.c | 283 ++++++++++++++++++++++++++++++++++++---
> > > > > 1 file changed, 267 insertions(+), 16 deletions(-)
> > > > >
> > > > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> > > > > index 486b5849033d..4de845d35bed 100644
> > > > > --- a/drivers/net/virtio_net.c
> > > > > +++ b/drivers/net/virtio_net.c
> > > > > @@ -126,6 +126,27 @@ static const struct virtnet_stat_desc virtnet_rq_stats_desc[] = {
> > > > > #define VIRTNET_SQ_STATS_LEN ARRAY_SIZE(virtnet_sq_stats_desc)
> > > > > #define VIRTNET_RQ_STATS_LEN ARRAY_SIZE(virtnet_rq_stats_desc)
> > > > >
> > > > > +/* The bufs on the same page may share this struct. */
> > > > > +struct virtnet_rq_dma {
> > > > > + struct virtnet_rq_dma *next;
> > > > > +
> > > > > + dma_addr_t addr;
> > > > > +
> > > > > + void *buf;
> > > > > + u32 len;
> > > > > +
> > > > > + u32 ref;
> > > > > +};
> > > > > +
> > > > > +/* Record the dma and buf. */
> > > >
> > > > I guess I see that. But why?
> > > > And these two comments are the extent of the available
> > > > documentation, that's not enough I feel.
> > > >
> > > >
> > > > > +struct virtnet_rq_data {
> > > > > + struct virtnet_rq_data *next;
> > > >
> > > > Is manually reimplementing a linked list the best
> > > > we can do?
> > >
> > > Yes, we can use llist.
> > >
> > > >
> > > > > +
> > > > > + void *buf;
> > > > > +
> > > > > + struct virtnet_rq_dma *dma;
> > > > > +};
> > > > > +
> > > > > /* Internal representation of a send virtqueue */
> > > > > struct send_queue {
> > > > > /* Virtqueue associated with this send _queue */
> > > > > @@ -175,6 +196,13 @@ struct receive_queue {
> > > > > char name[16];
> > > > >
> > > > > struct xdp_rxq_info xdp_rxq;
> > > > > +
> > > > > + struct virtnet_rq_data *data_array;
> > > > > + struct virtnet_rq_data *data_free;
> > > > > +
> > > > > + struct virtnet_rq_dma *dma_array;
> > > > > + struct virtnet_rq_dma *dma_free;
> > > > > + struct virtnet_rq_dma *last_dma;
> > > > > };
> > > > >
> > > > > /* This structure can contain rss message with maximum settings for indirection table and keysize
> > > > > @@ -549,6 +577,176 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> > > > > return skb;
> > > > > }
> > > > >
> > > > > +static void virtnet_rq_unmap(struct receive_queue *rq, struct virtnet_rq_dma *dma)
> > > > > +{
> > > > > + struct device *dev;
> > > > > +
> > > > > + --dma->ref;
> > > > > +
> > > > > + if (dma->ref)
> > > > > + return;
> > > > > +
> > > >
> > > > If you don't unmap there is no guarantee valid data will be
> > > > there in the buffer.
> > > >
> > > > > + dev = virtqueue_dma_dev(rq->vq);
> > > > > +
> > > > > + dma_unmap_page(dev, dma->addr, dma->len, DMA_FROM_DEVICE);
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > > +
> > > > > + dma->next = rq->dma_free;
> > > > > + rq->dma_free = dma;
> > > > > +}
> > > > > +
> > > > > +static void *virtnet_rq_recycle_data(struct receive_queue *rq,
> > > > > + struct virtnet_rq_data *data)
> > > > > +{
> > > > > + void *buf;
> > > > > +
> > > > > + buf = data->buf;
> > > > > +
> > > > > + data->next = rq->data_free;
> > > > > + rq->data_free = data;
> > > > > +
> > > > > + return buf;
> > > > > +}
> > > > > +
> > > > > +static struct virtnet_rq_data *virtnet_rq_get_data(struct receive_queue *rq,
> > > > > + void *buf,
> > > > > + struct virtnet_rq_dma *dma)
> > > > > +{
> > > > > + struct virtnet_rq_data *data;
> > > > > +
> > > > > + data = rq->data_free;
> > > > > + rq->data_free = data->next;
> > > > > +
> > > > > + data->buf = buf;
> > > > > + data->dma = dma;
> > > > > +
> > > > > + return data;
> > > > > +}
> > > > > +
> > > > > +static void *virtnet_rq_get_buf(struct receive_queue *rq, u32 *len, void **ctx)
> > > > > +{
> > > > > + struct virtnet_rq_data *data;
> > > > > + void *buf;
> > > > > +
> > > > > + buf = virtqueue_get_buf_ctx(rq->vq, len, ctx);
> > > > > + if (!buf || !rq->data_array)
> > > > > + return buf;
> > > > > +
> > > > > + data = buf;
> > > > > +
> > > > > + virtnet_rq_unmap(rq, data->dma);
> > > > > +
> > > > > + return virtnet_rq_recycle_data(rq, data);
> > > > > +}
> > > > > +
> > > > > +static void *virtnet_rq_detach_unused_buf(struct receive_queue *rq)
> > > > > +{
> > > > > + struct virtnet_rq_data *data;
> > > > > + void *buf;
> > > > > +
> > > > > + buf = virtqueue_detach_unused_buf(rq->vq);
> > > > > + if (!buf || !rq->data_array)
> > > > > + return buf;
> > > > > +
> > > > > + data = buf;
> > > > > +
> > > > > + virtnet_rq_unmap(rq, data->dma);
> > > > > +
> > > > > + return virtnet_rq_recycle_data(rq, data);
> > > > > +}
> > > > > +
> > > > > +static int virtnet_rq_map_sg(struct receive_queue *rq, void *buf, u32 len)
> > > > > +{
> > > > > + struct virtnet_rq_dma *dma = rq->last_dma;
> > > > > + struct device *dev;
> > > > > + u32 off, map_len;
> > > > > + dma_addr_t addr;
> > > > > + void *end;
> > > > > +
> > > > > + if (likely(dma) && buf >= dma->buf && (buf + len <= dma->buf + dma->len)) {
> > > > > + ++dma->ref;
> > > > > + addr = dma->addr + (buf - dma->buf);
> > > > > + goto ok;
> > > > > + }
> > > >
> > > > So this is the meat of the proposed optimization. I guess that
> > > > if the last buffer we allocated happens to be in the same page
> > > > as this one then they can both be mapped for DMA together.
> > >
> > > Since we use page_frag, the buffers we allocated are all continuous.
> > >
> > > > Why last one specifically? Whether next one happens to
> > > > be close depends on luck. If you want to try optimizing this
> > > > the right thing to do is likely by using a page pool.
> > > > There's actually work upstream on page pool, look it up.
> > >
> > > As we discussed in another thread, the page pool is first used for xdp. Let's
> > > transform it step by step.
> > >
> > > Thanks.
> >
> > ok so this should wait then?
> >
> > > >
> > > > > +
> > > > > + end = buf + len - 1;
> > > > > + off = offset_in_page(end);
> > > > > + map_len = len + PAGE_SIZE - off;
> > > > > +
> > > > > + dev = virtqueue_dma_dev(rq->vq);
> > > > > +
> > > > > + addr = dma_map_page_attrs(dev, virt_to_page(buf), offset_in_page(buf),
> > > > > + map_len, DMA_FROM_DEVICE, 0);
> > > > > + if (addr == DMA_MAPPING_ERROR)
> > > > > + return -ENOMEM;
> > > > > +
> > > > > + dma = rq->dma_free;
> > > > > + rq->dma_free = dma->next;
> > > > > +
> > > > > + dma->ref = 1;
> > > > > + dma->buf = buf;
> > > > > + dma->addr = addr;
> > > > > + dma->len = map_len;
> > > > > +
> > > > > + rq->last_dma = dma;
> > > > > +
> > > > > +ok:
> > > > > + sg_init_table(rq->sg, 1);
> > > > > + rq->sg[0].dma_address = addr;
> > > > > + rq->sg[0].length = len;
> > > > > +
> > > > > + return 0;
> > > > > +}
> > > > > +
> > > > > +static int virtnet_rq_merge_map_init(struct virtnet_info *vi)
> > > > > +{
> > > > > + struct receive_queue *rq;
> > > > > + int i, err, j, num;
> > > > > +
> > > > > + /* disable for big mode */
> > > > > + if (!vi->mergeable_rx_bufs && vi->big_packets)
> > > > > + return 0;
> > > > > +
> > > > > + for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > > + err = virtqueue_set_premapped(vi->rq[i].vq);
> > > > > + if (err)
> > > > > + continue;
> > > > > +
> > > > > + rq = &vi->rq[i];
> > > > > +
> > > > > + num = virtqueue_get_vring_size(rq->vq);
> > > > > +
> > > > > + rq->data_array = kmalloc_array(num, sizeof(*rq->data_array), GFP_KERNEL);
> > > > > + if (!rq->data_array)
> > > > > + goto err;
> > > > > +
> > > > > + rq->dma_array = kmalloc_array(num, sizeof(*rq->dma_array), GFP_KERNEL);
> > > > > + if (!rq->dma_array)
> > > > > + goto err;
> > > > > +
> > > > > + for (j = 0; j < num; ++j) {
> > > > > + rq->data_array[j].next = rq->data_free;
> > > > > + rq->data_free = &rq->data_array[j];
> > > > > +
> > > > > + rq->dma_array[j].next = rq->dma_free;
> > > > > + rq->dma_free = &rq->dma_array[j];
> > > > > + }
> > > > > + }
> > > > > +
> > > > > + return 0;
> > > > > +
> > > > > +err:
> > > > > + for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > > + struct receive_queue *rq;
> > > > > +
> > > > > + rq = &vi->rq[i];
> > > > > +
> > > > > + kfree(rq->dma_array);
> > > > > + kfree(rq->data_array);
> > > > > + }
> > > > > +
> > > > > + return -ENOMEM;
> > > > > +}
> > > > > +
> > > > > static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi)
> > > > > {
> > > > > unsigned int len;
> > > > > @@ -835,7 +1033,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> > > > > void *buf;
> > > > > int off;
> > > > >
> > > > > - buf = virtqueue_get_buf(rq->vq, &buflen);
> > > > > + buf = virtnet_rq_get_buf(rq, &buflen, NULL);
> > > > > if (unlikely(!buf))
> > > > > goto err_buf;
> > > > >
> > > > > @@ -1126,7 +1324,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> > > > > return -EINVAL;
> > > > >
> > > > > while (--*num_buf > 0) {
> > > > > - buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > > > > + buf = virtnet_rq_get_buf(rq, &len, &ctx);
> > > > > if (unlikely(!buf)) {
> > > > > pr_debug("%s: rx error: %d buffers out of %d missing\n",
> > > > > dev->name, *num_buf,
> > > > > @@ -1351,7 +1549,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > > > > while (--num_buf) {
> > > > > int num_skb_frags;
> > > > >
> > > > > - buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx);
> > > > > + buf = virtnet_rq_get_buf(rq, &len, &ctx);
> > > > > if (unlikely(!buf)) {
> > > > > pr_debug("%s: rx error: %d buffers out of %d missing\n",
> > > > > dev->name, num_buf,
> > > > > @@ -1414,7 +1612,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> > > > > err_skb:
> > > > > put_page(page);
> > > > > while (num_buf-- > 1) {
> > > > > - buf = virtqueue_get_buf(rq->vq, &len);
> > > > > + buf = virtnet_rq_get_buf(rq, &len, NULL);
> > > > > if (unlikely(!buf)) {
> > > > > pr_debug("%s: rx error: %d buffers missing\n",
> > > > > dev->name, num_buf);
> > > > > @@ -1529,6 +1727,7 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> > > > > unsigned int xdp_headroom = virtnet_get_headroom(vi);
> > > > > void *ctx = (void *)(unsigned long)xdp_headroom;
> > > > > int len = vi->hdr_len + VIRTNET_RX_PAD + GOOD_PACKET_LEN + xdp_headroom;
> > > > > + struct virtnet_rq_data *data;
> > > > > int err;
> > > > >
> > > > > len = SKB_DATA_ALIGN(len) +
> > > > > @@ -1539,11 +1738,34 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
> > > > > buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> > > > > get_page(alloc_frag->page);
> > > > > alloc_frag->offset += len;
> > > > > - sg_init_one(rq->sg, buf + VIRTNET_RX_PAD + xdp_headroom,
> > > > > - vi->hdr_len + GOOD_PACKET_LEN);
> > > > > - err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > > > > +
> > > > > + if (rq->data_array) {
> > > > > + err = virtnet_rq_map_sg(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
> > > > > + vi->hdr_len + GOOD_PACKET_LEN);
> > > > > + if (err)
> > > > > + goto map_err;
> > > > > +
> > > > > + data = virtnet_rq_get_data(rq, buf, rq->last_dma);
> > > > > + } else {
> > > > > + sg_init_one(rq->sg, buf + VIRTNET_RX_PAD + xdp_headroom,
> > > > > + vi->hdr_len + GOOD_PACKET_LEN);
> > > > > + data = (void *)buf;
> > > > > + }
> > > > > +
> > > > > + err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, data, ctx, gfp);
> > > > > if (err < 0)
> > > > > - put_page(virt_to_head_page(buf));
> > > > > + goto add_err;
> > > > > +
> > > > > + return err;
> > > > > +
> > > > > +add_err:
> > > > > + if (rq->data_array) {
> > > > > + virtnet_rq_unmap(rq, data->dma);
> > > > > + virtnet_rq_recycle_data(rq, data);
> > > > > + }
> > > > > +
> > > > > +map_err:
> > > > > + put_page(virt_to_head_page(buf));
> > > > > return err;
> > > > > }
> > > > >
> > > > > @@ -1620,6 +1842,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > > > > unsigned int headroom = virtnet_get_headroom(vi);
> > > > > unsigned int tailroom = headroom ? sizeof(struct skb_shared_info) : 0;
> > > > > unsigned int room = SKB_DATA_ALIGN(headroom + tailroom);
> > > > > + struct virtnet_rq_data *data;
> > > > > char *buf;
> > > > > void *ctx;
> > > > > int err;
> > > > > @@ -1650,12 +1873,32 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> > > > > alloc_frag->offset += hole;
> > > > > }
> > > > >
> > > > > - sg_init_one(rq->sg, buf, len);
> > > > > + if (rq->data_array) {
> > > > > + err = virtnet_rq_map_sg(rq, buf, len);
> > > > > + if (err)
> > > > > + goto map_err;
> > > > > +
> > > > > + data = virtnet_rq_get_data(rq, buf, rq->last_dma);
> > > > > + } else {
> > > > > + sg_init_one(rq->sg, buf, len);
> > > > > + data = (void *)buf;
> > > > > + }
> > > > > +
> > > > > ctx = mergeable_len_to_ctx(len + room, headroom);
> > > > > - err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> > > > > + err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, data, ctx, gfp);
> > > > > if (err < 0)
> > > > > - put_page(virt_to_head_page(buf));
> > > > > + goto add_err;
> > > > > +
> > > > > + return 0;
> > > > > +
> > > > > +add_err:
> > > > > + if (rq->data_array) {
> > > > > + virtnet_rq_unmap(rq, data->dma);
> > > > > + virtnet_rq_recycle_data(rq, data);
> > > > > + }
> > > > >
> > > > > +map_err:
> > > > > + put_page(virt_to_head_page(buf));
> > > > > return err;
> > > > > }
> > > > >
> > > > > @@ -1775,13 +2018,13 @@ static int virtnet_receive(struct receive_queue *rq, int budget,
> > > > > void *ctx;
> > > > >
> > > > > while (stats.packets < budget &&
> > > > > - (buf = virtqueue_get_buf_ctx(rq->vq, &len, &ctx))) {
> > > > > + (buf = virtnet_rq_get_buf(rq, &len, &ctx))) {
> > > > > receive_buf(vi, rq, buf, len, ctx, xdp_xmit, &stats);
> > > > > stats.packets++;
> > > > > }
> > > > > } else {
> > > > > while (stats.packets < budget &&
> > > > > - (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
> > > > > + (buf = virtnet_rq_get_buf(rq, &len, NULL)) != NULL) {
> > > > > receive_buf(vi, rq, buf, len, NULL, xdp_xmit, &stats);
> > > > > stats.packets++;
> > > > > }
> > > > > @@ -3514,6 +3757,9 @@ static void virtnet_free_queues(struct virtnet_info *vi)
> > > > > for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > > __netif_napi_del(&vi->rq[i].napi);
> > > > > __netif_napi_del(&vi->sq[i].napi);
> > > > > +
> > > > > + kfree(vi->rq[i].data_array);
> > > > > + kfree(vi->rq[i].dma_array);
> > > > > }
> > > > >
> > > > > /* We called __netif_napi_del(),
> > > > > @@ -3591,9 +3837,10 @@ static void free_unused_bufs(struct virtnet_info *vi)
> > > > > }
> > > > >
> > > > > for (i = 0; i < vi->max_queue_pairs; i++) {
> > > > > - struct virtqueue *vq = vi->rq[i].vq;
> > > > > - while ((buf = virtqueue_detach_unused_buf(vq)) != NULL)
> > > > > - virtnet_rq_free_unused_buf(vq, buf);
> > > > > + struct receive_queue *rq = &vi->rq[i];
> > > > > +
> > > > > + while ((buf = virtnet_rq_detach_unused_buf(rq)) != NULL)
> > > > > + virtnet_rq_free_unused_buf(rq->vq, buf);
> > > > > cond_resched();
> > > > > }
> > > > > }
> > > > > @@ -3767,6 +4014,10 @@ static int init_vqs(struct virtnet_info *vi)
> > > > > if (ret)
> > > > > goto err_free;
> > > > >
> > > > > + ret = virtnet_rq_merge_map_init(vi);
> > > > > + if (ret)
> > > > > + goto err_free;
> > > > > +
> > > > > cpus_read_lock();
> > > > > virtnet_set_affinity(vi);
> > > > > cpus_read_unlock();
> > > > > --
> > > > > 2.32.0.3.g01195cf9f
> > > >
> >
>
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