Subject: Re: [PATCH net-next 2/5] virtio_net: Add page_pool support to improve performance

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sun, 28 May 2023 02:40:27 -0400

On Sat, May 27, 2023 at 08:35:01PM +0800, Liang Chen wrote:
> On Fri, May 26, 2023 at 2:51 PM Jason Wang <[email-masked]> wrote:
> >
> > On Fri, May 26, 2023 at 1:46 PM Liang Chen <[email-masked]> 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.
> >
> 
> Sure, I will include that on v2.
> > > 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?
> >
> 
> Thank you for raising the point. It does make sense to enable it by default.

I'd like to see more benchmarks pls then, with a variety of packet
sizes, udp and tcp.

> > >
> > > 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.
> >
> 
> Sure. It will be added on v2.
> > >
> > > With this foundation, we can further integrate page pool fragmentation and
> > > DMA map/unmap support.
> > >
> > > Signed-off-by: Liang Chen <[email-masked]>
> > > ---
> > >  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.
> >
> 
> Sure. it will be done on v2.
> > >  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?
> 
> Yeah, it has the queue_index there.
> >
> > >         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?
> >
> 
> Sorry, I don't quite understand the point here. Would you please
> elaborate a bit more?
> > >                         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.
> >
> 
> Sure. Will do that on v2.
> > > +                       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
> >
> 
> Big mode uses the page chain to recycle pages, thus the using of
> "private" of the buffer page. I will take further look into that to
> see if it is better to use page pool in these cases. 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
> > >
> >