Michael S. Tsirkin
2023-Jul-10 11:59 UTC
[PATCH vhost v11 10/10] virtio_net: merge dma operation for one page
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 at redhat.com> 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. Try e.g. bounce buffer. Which is where you will see a problem: your patches won't work.> > > > > Signed-off-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com> > > > > 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 > >
Xuan Zhuo
2023-Jul-10 12:38 UTC
[PATCH vhost v11 10/10] virtio_net: merge dma operation for one page
On Mon, 10 Jul 2023 07:59:03 -0400, "Michael S. Tsirkin" <mst at redhat.com> 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 at redhat.com> 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. 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 at linux.alibaba.com> > > > > > > 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 > > > >