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Date: Fri, 26 May 2023 14:50:49 +0800
From: Jason Wang <jasowang@...hat.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: mst@...hat.com, virtualization@...ts.linux-foundation.org,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
xuanzhuo@...ux.alibaba.com, kuba@...nel.org, edumazet@...gle.com,
davem@...emloft.net, pabeni@...hat.com, alexander.duyck@...il.com
Subject: Re: [PATCH net-next 2/5] virtio_net: Add page_pool support to improve performance
On Fri, May 26, 2023 at 1:46 PM Liang Chen <liangchen.linux@...il.com> wrote:
>
> The implementation at the moment uses one page per packet in both the
> normal and XDP path.
It's better to explain why we need a page pool and how it can help the
performance.
> In addition, introducing a module parameter to enable
> or disable the usage of page pool (disabled by default).
If page pool wins for most of the cases, any reason to disable it by default?
>
> In single-core vm testing environments, it gives a modest performance gain
> in the normal path.
> Upstream codebase: 47.5 Gbits/sec
> Upstream codebase + page_pool support: 50.2 Gbits/sec
>
> In multi-core vm testing environments, The most significant performance
> gain is observed in XDP cpumap:
> Upstream codebase: 1.38 Gbits/sec
> Upstream codebase + page_pool support: 9.74 Gbits/sec
Please show more details on the test. E.g which kinds of tests have
you measured?
Btw, it would be better to measure PPS as well.
>
> With this foundation, we can further integrate page pool fragmentation and
> DMA map/unmap support.
>
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
> ---
> drivers/net/virtio_net.c | 188 ++++++++++++++++++++++++++++++---------
I believe we should make virtio-net to select CONFIG_PAGE_POOL or do
the ifdef tricks at least.
> 1 file changed, 146 insertions(+), 42 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index c5dca0d92e64..99c0ca0c1781 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -31,6 +31,9 @@ module_param(csum, bool, 0444);
> module_param(gso, bool, 0444);
> module_param(napi_tx, bool, 0644);
>
> +static bool page_pool_enabled;
> +module_param(page_pool_enabled, bool, 0400);
> +
> /* FIXME: MTU in config. */
> #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
> #define GOOD_COPY_LEN 128
> @@ -159,6 +162,9 @@ struct receive_queue {
> /* Chain pages by the private ptr. */
> struct page *pages;
>
> + /* Page pool */
> + struct page_pool *page_pool;
> +
> /* Average packet length for mergeable receive buffers. */
> struct ewma_pkt_len mrg_avg_pkt_len;
>
> @@ -459,6 +465,14 @@ static struct sk_buff *virtnet_build_skb(void *buf, unsigned int buflen,
> return skb;
> }
>
> +static void virtnet_put_page(struct receive_queue *rq, struct page *page)
> +{
> + if (rq->page_pool)
> + page_pool_put_full_page(rq->page_pool, page, true);
> + else
> + put_page(page);
> +}
> +
> /* Called from bottom half context */
> static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> struct receive_queue *rq,
> @@ -555,7 +569,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
> hdr = skb_vnet_hdr(skb);
> memcpy(hdr, hdr_p, hdr_len);
> if (page_to_free)
> - put_page(page_to_free);
> + virtnet_put_page(rq, page_to_free);
>
> return skb;
> }
> @@ -802,7 +816,7 @@ static int virtnet_xdp_xmit(struct net_device *dev,
> return ret;
> }
>
> -static void put_xdp_frags(struct xdp_buff *xdp)
> +static void put_xdp_frags(struct xdp_buff *xdp, struct receive_queue *rq)
> {
rq could be fetched from xdp_rxq_info?
> struct skb_shared_info *shinfo;
> struct page *xdp_page;
> @@ -812,7 +826,7 @@ static void put_xdp_frags(struct xdp_buff *xdp)
> shinfo = xdp_get_shared_info_from_buff(xdp);
> for (i = 0; i < shinfo->nr_frags; i++) {
> xdp_page = skb_frag_page(&shinfo->frags[i]);
> - put_page(xdp_page);
> + virtnet_put_page(rq, xdp_page);
> }
> }
> }
> @@ -903,7 +917,11 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> if (page_off + *len + tailroom > PAGE_SIZE)
> return NULL;
>
> - page = alloc_page(GFP_ATOMIC);
> + if (rq->page_pool)
> + page = page_pool_dev_alloc_pages(rq->page_pool);
> + else
> + page = alloc_page(GFP_ATOMIC);
> +
> if (!page)
> return NULL;
>
> @@ -926,21 +944,24 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> * is sending packet larger than the MTU.
> */
> if ((page_off + buflen + tailroom) > PAGE_SIZE) {
> - put_page(p);
> + virtnet_put_page(rq, p);
> goto err_buf;
> }
>
> memcpy(page_address(page) + page_off,
> page_address(p) + off, buflen);
> page_off += buflen;
> - put_page(p);
> + virtnet_put_page(rq, p);
> }
>
> /* Headroom does not contribute to packet length */
> *len = page_off - VIRTIO_XDP_HEADROOM;
> return page;
> err_buf:
> - __free_pages(page, 0);
> + if (rq->page_pool)
> + page_pool_put_full_page(rq->page_pool, page, true);
> + else
> + __free_pages(page, 0);
> return NULL;
> }
>
> @@ -1144,7 +1165,7 @@ static void mergeable_buf_free(struct receive_queue *rq, int num_buf,
> }
> stats->bytes += len;
> page = virt_to_head_page(buf);
> - put_page(page);
> + virtnet_put_page(rq, page);
> }
> }
>
> @@ -1264,7 +1285,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> cur_frag_size = truesize;
> xdp_frags_truesz += cur_frag_size;
> if (unlikely(len > truesize - room || cur_frag_size > PAGE_SIZE)) {
> - put_page(page);
> + virtnet_put_page(rq, page);
> pr_debug("%s: rx error: len %u exceeds truesize %lu\n",
> dev->name, len, (unsigned long)(truesize - room));
> dev->stats.rx_length_errors++;
> @@ -1283,7 +1304,7 @@ static int virtnet_build_xdp_buff_mrg(struct net_device *dev,
> return 0;
>
> err:
> - put_xdp_frags(xdp);
> + put_xdp_frags(xdp, rq);
> return -EINVAL;
> }
>
> @@ -1344,7 +1365,10 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> if (*len + xdp_room > PAGE_SIZE)
> return NULL;
>
> - xdp_page = alloc_page(GFP_ATOMIC);
> + if (rq->page_pool)
> + xdp_page = page_pool_dev_alloc_pages(rq->page_pool);
> + else
> + xdp_page = alloc_page(GFP_ATOMIC);
> if (!xdp_page)
> return NULL;
>
> @@ -1354,7 +1378,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>
> *frame_sz = PAGE_SIZE;
>
> - put_page(*page);
> + virtnet_put_page(rq, *page);
>
> *page = xdp_page;
>
> @@ -1400,6 +1424,8 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> head_skb = build_skb_from_xdp_buff(dev, vi, &xdp, xdp_frags_truesz);
> if (unlikely(!head_skb))
> break;
> + if (rq->page_pool)
> + skb_mark_for_recycle(head_skb);
> return head_skb;
>
> case XDP_TX:
> @@ -1410,10 +1436,10 @@ static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> break;
> }
>
> - put_xdp_frags(&xdp);
> + put_xdp_frags(&xdp, rq);
>
> err_xdp:
> - put_page(page);
> + virtnet_put_page(rq, page);
> mergeable_buf_free(rq, num_buf, dev, stats);
>
> stats->xdp_drops++;
> @@ -1467,6 +1493,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> head_skb = page_to_skb(vi, rq, page, offset, len, truesize, headroom);
> curr_skb = head_skb;
>
> + if (rq->page_pool)
> + skb_mark_for_recycle(curr_skb);
> +
> if (unlikely(!curr_skb))
> goto err_skb;
> while (--num_buf) {
> @@ -1509,6 +1538,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> curr_skb = nskb;
> head_skb->truesize += nskb->truesize;
> num_skb_frags = 0;
> + if (rq->page_pool)
> + skb_mark_for_recycle(curr_skb);
> }
> if (curr_skb != head_skb) {
> head_skb->data_len += len;
> @@ -1517,7 +1548,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> }
> offset = buf - page_address(page);
> if (skb_can_coalesce(curr_skb, num_skb_frags, page, offset)) {
> - put_page(page);
> + virtnet_put_page(rq, page);
I wonder why not we can't do this during buffer allocation like other drivers?
> skb_coalesce_rx_frag(curr_skb, num_skb_frags - 1,
> len, truesize);
> } else {
> @@ -1530,7 +1561,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
> return head_skb;
>
> err_skb:
> - put_page(page);
> + virtnet_put_page(rq, page);
> mergeable_buf_free(rq, num_buf, dev, stats);
>
> err_buf:
> @@ -1737,31 +1768,40 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> * disabled GSO for XDP, it won't be a big issue.
> */
> len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> - if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
> - return -ENOMEM;
> + if (rq->page_pool) {
> + struct page *page;
>
> - buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> - buf += headroom; /* advance address leaving hole at front of pkt */
> - get_page(alloc_frag->page);
> - alloc_frag->offset += len + room;
> - hole = alloc_frag->size - alloc_frag->offset;
> - if (hole < len + room) {
> - /* To avoid internal fragmentation, if there is very likely not
> - * enough space for another buffer, add the remaining space to
> - * the current buffer.
> - * XDP core assumes that frame_size of xdp_buff and the length
> - * of the frag are PAGE_SIZE, so we disable the hole mechanism.
> - */
> - if (!headroom)
> - len += hole;
> - alloc_frag->offset += hole;
> - }
> + page = page_pool_dev_alloc_pages(rq->page_pool);
> + if (unlikely(!page))
> + return -ENOMEM;
> + buf = (char *)page_address(page);
> + buf += headroom; /* advance address leaving hole at front of pkt */
> + } else {
> + if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
Why not simply use a helper like virtnet_page_frag_refill() and add
the page_pool allocation logic there? It helps to reduce the
changeset.
> + return -ENOMEM;
>
> + buf = (char *)page_address(alloc_frag->page) + alloc_frag->offset;
> + buf += headroom; /* advance address leaving hole at front of pkt */
> + get_page(alloc_frag->page);
> + alloc_frag->offset += len + room;
> + hole = alloc_frag->size - alloc_frag->offset;
> + if (hole < len + room) {
> + /* To avoid internal fragmentation, if there is very likely not
> + * enough space for another buffer, add the remaining space to
> + * the current buffer.
> + * XDP core assumes that frame_size of xdp_buff and the length
> + * of the frag are PAGE_SIZE, so we disable the hole mechanism.
> + */
> + if (!headroom)
> + len += hole;
> + alloc_frag->offset += hole;
> + }
> + }
> sg_init_one(rq->sg, buf, len);
> ctx = mergeable_len_to_ctx(len + room, headroom);
> err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
> if (err < 0)
> - put_page(virt_to_head_page(buf));
> + virtnet_put_page(rq, virt_to_head_page(buf));
>
> return err;
> }
> @@ -1994,8 +2034,15 @@ static int virtnet_enable_queue_pair(struct virtnet_info *vi, int qp_index)
> if (err < 0)
> return err;
>
> - err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
> - MEM_TYPE_PAGE_SHARED, NULL);
> + if (vi->rq[qp_index].page_pool)
> + err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
> + MEM_TYPE_PAGE_POOL,
> + vi->rq[qp_index].page_pool);
> + else
> + err = xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xdp_rxq,
> + MEM_TYPE_PAGE_SHARED,
> + NULL);
> +
> if (err < 0)
> goto err_xdp_reg_mem_model;
>
> @@ -2951,6 +2998,7 @@ static void virtnet_get_strings(struct net_device *dev, u32 stringset, u8 *data)
> ethtool_sprintf(&p, "tx_queue_%u_%s", i,
> virtnet_sq_stats_desc[j].desc);
> }
> + page_pool_ethtool_stats_get_strings(p);
> break;
> }
> }
> @@ -2962,12 +3010,30 @@ static int virtnet_get_sset_count(struct net_device *dev, int sset)
> switch (sset) {
> case ETH_SS_STATS:
> return vi->curr_queue_pairs * (VIRTNET_RQ_STATS_LEN +
> - VIRTNET_SQ_STATS_LEN);
> + VIRTNET_SQ_STATS_LEN +
> + (page_pool_enabled && vi->mergeable_rx_bufs ?
> + page_pool_ethtool_stats_get_count() : 0));
> default:
> return -EOPNOTSUPP;
> }
> }
>
> +static void virtnet_get_page_pool_stats(struct net_device *dev, u64 *data)
> +{
> +#ifdef CONFIG_PAGE_POOL_STATS
> + struct virtnet_info *vi = netdev_priv(dev);
> + struct page_pool_stats pp_stats = {};
> + int i;
> +
> + for (i = 0; i < vi->curr_queue_pairs; i++) {
> + if (!vi->rq[i].page_pool)
> + continue;
> + page_pool_get_stats(vi->rq[i].page_pool, &pp_stats);
> + }
> + page_pool_ethtool_stats_get(data, &pp_stats);
> +#endif /* CONFIG_PAGE_POOL_STATS */
> +}
> +
> static void virtnet_get_ethtool_stats(struct net_device *dev,
> struct ethtool_stats *stats, u64 *data)
> {
> @@ -3003,6 +3069,8 @@ static void virtnet_get_ethtool_stats(struct net_device *dev,
> } while (u64_stats_fetch_retry(&sq->stats.syncp, start));
> idx += VIRTNET_SQ_STATS_LEN;
> }
> +
> + virtnet_get_page_pool_stats(dev, &data[idx]);
> }
>
> static void virtnet_get_channels(struct net_device *dev,
> @@ -3623,6 +3691,8 @@ 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);
> + if (vi->rq[i].page_pool)
> + page_pool_destroy(vi->rq[i].page_pool);
> }
>
> /* We called __netif_napi_del(),
> @@ -3679,12 +3749,19 @@ static void virtnet_rq_free_unused_buf(struct virtqueue *vq, void *buf)
> struct virtnet_info *vi = vq->vdev->priv;
> int i = vq2rxq(vq);
>
> - if (vi->mergeable_rx_bufs)
> - put_page(virt_to_head_page(buf));
> - else if (vi->big_packets)
> + if (vi->mergeable_rx_bufs) {
> + if (vi->rq[i].page_pool) {
> + page_pool_put_full_page(vi->rq[i].page_pool,
> + virt_to_head_page(buf),
> + true);
> + } else {
> + put_page(virt_to_head_page(buf));
> + }
> + } else if (vi->big_packets) {
> give_pages(&vi->rq[i], buf);
Any reason only mergeable were modified but not for small and big?
Thanks
> - else
> + } else {
> put_page(virt_to_head_page(buf));
> + }
> }
>
> static void free_unused_bufs(struct virtnet_info *vi)
> @@ -3718,6 +3795,26 @@ static void virtnet_del_vqs(struct virtnet_info *vi)
> virtnet_free_queues(vi);
> }
>
> +static void virtnet_alloc_page_pool(struct receive_queue *rq)
> +{
> + struct virtio_device *vdev = rq->vq->vdev;
> +
> + struct page_pool_params pp_params = {
> + .order = 0,
> + .pool_size = rq->vq->num_max,
> + .nid = dev_to_node(vdev->dev.parent),
> + .dev = vdev->dev.parent,
> + .offset = 0,
> + };
> +
> + rq->page_pool = page_pool_create(&pp_params);
> + if (IS_ERR(rq->page_pool)) {
> + dev_warn(&vdev->dev, "page pool creation failed: %ld\n",
> + PTR_ERR(rq->page_pool));
> + rq->page_pool = NULL;
> + }
> +}
> +
> /* How large should a single buffer be so a queue full of these can fit at
> * least one full packet?
> * Logic below assumes the mergeable buffer header is used.
> @@ -3801,6 +3898,13 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
> vi->rq[i].vq = vqs[rxq2vq(i)];
> vi->rq[i].min_buf_len = mergeable_min_buf_len(vi, vi->rq[i].vq);
> vi->sq[i].vq = vqs[txq2vq(i)];
> +
> + if (page_pool_enabled && vi->mergeable_rx_bufs)
> + virtnet_alloc_page_pool(&vi->rq[i]);
> + else
> + dev_warn(&vi->vdev->dev,
> + "page pool only support mergeable mode\n");
> +
> }
>
> /* run here: ret == 0. */
> --
> 2.31.1
>
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