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Message-ID: <CACGkMEtoiHXese1sNJELeidmFc6nFR8rE1aA8MooaEKKUSw_eg@mail.gmail.com>
Date: Thu, 13 Jul 2023 12:20:01 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
Cc: virtualization@...ts.linux-foundation.org,
"Michael S. Tsirkin" <mst@...hat.com>, "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>, netdev@...r.kernel.org, bpf@...r.kernel.org,
Christoph Hellwig <hch@...radead.org>
Subject: Re: [PATCH vhost v11 10/10] virtio_net: merge dma operation for one page
On Mon, Jul 10, 2023 at 11:43 AM Xuan Zhuo <xuanzhuo@...ux.alibaba.com> wrote:
>
I'd suggest to tweak the title like:
"merge dma operations when refilling mergeable buffers"
> Currently, the virtio core will perform a dma operation for each
> operation.
"for each buffer"?
> 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%.
Btw, it looks to me the code to deal with XDP_TX/REDIRECT for
linearized pages was missed.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> 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. */
> +struct virtnet_rq_data {
> + struct virtnet_rq_data *next;
> +
> + 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;
> +
> + 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;
> + }
> +
> + end = buf + len - 1;
> + off = offset_in_page(end);
> + map_len = len + PAGE_SIZE - off;
This assumes a PAGE_SIZE which seems sub-optimal as page frag could be
larger than this.
> +
> + 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)
Can we avoid those allocations when we don't use the DMA API?
> + 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);
Thanks to the compound page. I wonder if everything could be
simplified if we just reuse page->private for storing metadata like
dma address and refcnt. Then we don't need extra stuff for tracking
any other thing?
Thanks
> + 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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