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From:   Liang Chen <liangchen.linux@gmail.com>
Date:   Sat, 27 May 2023 20:35:01 +0800
Message-ID: <CAKhg4tL2b9LEsaNuLi94Zf9XQ4S2FyoXWzW9wTTkrU8L1qNQcQ@mail.gmail.com>
Subject: Re: [PATCH net-next 2/5] virtio_net: Add page_pool support to improve performance
To:     Jason Wang <jasowang@redhat.com>
Cc:     mst@redhat.com, virtualization@lists.linux-foundation.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        xuanzhuo@linux.alibaba.com, kuba@kernel.org, edumazet@google.com,
        davem@davemloft.net, pabeni@redhat.com, alexander.duyck@gmail.com
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On Fri, May 26, 2023 at 2:51=E2=80=AFPM Jason Wang <jasowang@redhat.com> wr=
ote:
>
> On Fri, May 26, 2023 at 1:46=E2=80=AFPM Liang Chen <liangchen.linux@gmail=
.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.
>

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 defa=
ult?
>

Thank you for raising the point. It does make sense to enable it by default=
.
> >
> > In single-core vm testing environments, it gives a modest performance g=
ain
> > 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 <liangchen.linux@gmail.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.
>

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 *pa=
ge)
> > +{
> > +       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_i=
nfo *vi,
> >         hdr =3D 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 =3D xdp_get_shared_info_from_buff(xdp);
> >                 for (i =3D 0; i < shinfo->nr_frags; i++) {
> >                         xdp_page =3D 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 rece=
ive_queue *rq,
> >         if (page_off + *len + tailroom > PAGE_SIZE)
> >                 return NULL;
> >
> > -       page =3D alloc_page(GFP_ATOMIC);
> > +       if (rq->page_pool)
> > +               page =3D page_pool_dev_alloc_pages(rq->page_pool);
> > +       else
> > +               page =3D alloc_page(GFP_ATOMIC);
> > +
> >         if (!page)
> >                 return NULL;
> >
> > @@ -926,21 +944,24 @@ static struct page *xdp_linearize_page(struct rec=
eive_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 +=3D buflen;
> > -               put_page(p);
> > +               virtnet_put_page(rq, p);
> >         }
> >
> >         /* Headroom does not contribute to packet length */
> >         *len =3D 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_que=
ue *rq, int num_buf,
> >                 }
> >                 stats->bytes +=3D len;
> >                 page =3D 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 =3D truesize;
> >                 xdp_frags_truesz +=3D cur_frag_size;
> >                 if (unlikely(len > truesize - room || cur_frag_size > P=
AGE_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)(truesi=
ze - 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 virtne=
t_info *vi,
> >                 if (*len + xdp_room > PAGE_SIZE)
> >                         return NULL;
> >
> > -               xdp_page =3D alloc_page(GFP_ATOMIC);
> > +               if (rq->page_pool)
> > +                       xdp_page =3D page_pool_dev_alloc_pages(rq->page=
_pool);
> > +               else
> > +                       xdp_page =3D 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 =3D PAGE_SIZE;
> >
> > -       put_page(*page);
> > +       virtnet_put_page(rq, *page);
> >
> >         *page =3D xdp_page;
> >
> > @@ -1400,6 +1424,8 @@ static struct sk_buff *receive_mergeable_xdp(stru=
ct net_device *dev,
> >                 head_skb =3D 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(st=
ruct 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 n=
et_device *dev,
> >         head_skb =3D page_to_skb(vi, rq, page, offset, len, truesize, h=
eadroom);
> >         curr_skb =3D 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 n=
et_device *dev,
> >                         curr_skb =3D nskb;
> >                         head_skb->truesize +=3D nskb->truesize;
> >                         num_skb_frags =3D 0;
> > +                       if (rq->page_pool)
> > +                               skb_mark_for_recycle(curr_skb);
> >                 }
> >                 if (curr_skb !=3D head_skb) {
> >                         head_skb->data_len +=3D len;
> > @@ -1517,7 +1548,7 @@ static struct sk_buff *receive_mergeable(struct n=
et_device *dev,
> >                 }
> >                 offset =3D buf - page_address(page);
> >                 if (skb_can_coalesce(curr_skb, num_skb_frags, page, off=
set)) {
> > -                       put_page(page);
> > +                       virtnet_put_page(rq, page);
>
> I wonder why not we can't do this during buffer allocation like other dri=
vers?
>

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 n=
et_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 =3D 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 =3D (char *)page_address(alloc_frag->page) + alloc_frag->of=
fset;
> > -       buf +=3D headroom; /* advance address leaving hole at front of =
pkt */
> > -       get_page(alloc_frag->page);
> > -       alloc_frag->offset +=3D len + room;
> > -       hole =3D alloc_frag->size - alloc_frag->offset;
> > -       if (hole < len + room) {
> > -               /* To avoid internal fragmentation, if there is very li=
kely not
> > -                * enough space for another buffer, add the remaining s=
pace 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 me=
chanism.
> > -                */
> > -               if (!headroom)
> > -                       len +=3D hole;
> > -               alloc_frag->offset +=3D hole;
> > -       }
> > +               page =3D page_pool_dev_alloc_pages(rq->page_pool);
> > +               if (unlikely(!page))
> > +                       return -ENOMEM;
> > +               buf =3D (char *)page_address(page);
> > +               buf +=3D headroom; /* advance address leaving hole at f=
ront of pkt */
> > +       } else {
> > +               if (unlikely(!skb_page_frag_refill(len + room, alloc_fr=
ag, 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 =3D (char *)page_address(alloc_frag->page) + alloc_=
frag->offset;
> > +               buf +=3D headroom; /* advance address leaving hole at f=
ront of pkt */
> > +               get_page(alloc_frag->page);
> > +               alloc_frag->offset +=3D len + room;
> > +               hole =3D 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 rem=
aining 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 +=3D hole;
> > +                       alloc_frag->offset +=3D hole;
> > +               }
> > +       }
> >         sg_init_one(rq->sg, buf, len);
> >         ctx =3D mergeable_len_to_ctx(len + room, headroom);
> >         err =3D virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gf=
p);
> >         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 virt=
net_info *vi, int qp_index)
> >         if (err < 0)
> >                 return err;
> >
> > -       err =3D 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 =3D xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xd=
p_rxq,
> > +                                                MEM_TYPE_PAGE_POOL,
> > +                                                vi->rq[qp_index].page_=
pool);
> > +       else
> > +               err =3D xdp_rxq_info_reg_mem_model(&vi->rq[qp_index].xd=
p_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_de=
vice *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 && v=
i->mergeable_rx_bufs ?
> > +                                                page_pool_ethtool_stat=
s_get_count() : 0));
> >         default:
> >                 return -EOPNOTSUPP;
> >         }
> >  }
> >
> > +static void virtnet_get_page_pool_stats(struct net_device *dev, u64 *d=
ata)
> > +{
> > +#ifdef CONFIG_PAGE_POOL_STATS
> > +       struct virtnet_info *vi =3D netdev_priv(dev);
> > +       struct page_pool_stats pp_stats =3D {};
> > +       int i;
> > +
> > +       for (i =3D 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 +=3D 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_in=
fo *vi)
> >         for (i =3D 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 v=
irtqueue *vq, void *buf)
> >         struct virtnet_info *vi =3D vq->vdev->priv;
> >         int i =3D 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 =3D rq->vq->vdev;
> > +
> > +       struct page_pool_params pp_params =3D {
> > +               .order =3D 0,
> > +               .pool_size =3D rq->vq->num_max,
> > +               .nid =3D dev_to_node(vdev->dev.parent),
> > +               .dev =3D vdev->dev.parent,
> > +               .offset =3D 0,
> > +       };
> > +
> > +       rq->page_pool =3D 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 =3D NULL;
> > +       }
> > +}
> > +
> >  /* How large should a single buffer be so a queue full of these can fi=
t 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 =3D vqs[rxq2vq(i)];
> >                 vi->rq[i].min_buf_len =3D mergeable_min_buf_len(vi, vi-=
>rq[i].vq);
> >                 vi->sq[i].vq =3D 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 =3D=3D 0. */
> > --
> > 2.31.1
> >
>