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Date: Sun, 28 May 2023 02:25:21 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Liang Chen <liangchen.linux@...il.com>
Cc: jasowang@...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 3/5] virtio_net: Add page pool fragmentation
support
On Fri, May 26, 2023 at 01:46:19PM +0800, Liang Chen wrote:
> To further enhance performance, implement page pool fragmentation
> support and introduce a module parameter to enable or disable it.
>
> In single-core vm testing environments, there is an additional performance
> gain observed in the normal path compared to the one packet per page
> approach.
> Upstream codebase: 47.5 Gbits/sec
> Upstream codebase with page pool: 50.2 Gbits/sec
> Upstream codebase with page pool fragmentation support: 52.3 Gbits/sec
>
> There is also some performance gain for XDP cpumap.
> Upstream codebase: 1.38 Gbits/sec
> Upstream codebase with page pool: 9.74 Gbits/sec
> Upstream codebase with page pool fragmentation: 10.3 Gbits/sec
>
> Signed-off-by: Liang Chen <liangchen.linux@...il.com>
I think it's called fragmenting not fragmentation.
> ---
> drivers/net/virtio_net.c | 72 ++++++++++++++++++++++++++++++----------
> 1 file changed, 55 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 99c0ca0c1781..ac40b8c66c59 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -32,7 +32,9 @@ module_param(gso, bool, 0444);
> module_param(napi_tx, bool, 0644);
>
> static bool page_pool_enabled;
> +static bool page_pool_frag;
> module_param(page_pool_enabled, bool, 0400);
> +module_param(page_pool_frag, bool, 0400);
>
> /* FIXME: MTU in config. */
> #define GOOD_PACKET_LEN (ETH_HLEN + VLAN_HLEN + ETH_DATA_LEN)
So here again same questions.
-when is this a net perf gain when does it have no effect?
-can be on by default
- can we get rid of the extra modes?
> @@ -909,23 +911,32 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> struct page *p,
> int offset,
> int page_off,
> - unsigned int *len)
> + unsigned int *len,
> + unsigned int *pp_frag_offset)
> {
> int tailroom = SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> struct page *page;
> + unsigned int pp_frag_offset_val;
>
> if (page_off + *len + tailroom > PAGE_SIZE)
> return NULL;
>
> if (rq->page_pool)
> - page = page_pool_dev_alloc_pages(rq->page_pool);
> + if (rq->page_pool->p.flags & PP_FLAG_PAGE_FRAG)
> + page = page_pool_dev_alloc_frag(rq->page_pool, pp_frag_offset,
> + PAGE_SIZE);
> + else
> + page = page_pool_dev_alloc_pages(rq->page_pool);
> else
> page = alloc_page(GFP_ATOMIC);
>
> if (!page)
> return NULL;
>
> - memcpy(page_address(page) + page_off, page_address(p) + offset, *len);
> + pp_frag_offset_val = pp_frag_offset ? *pp_frag_offset : 0;
> +
> + memcpy(page_address(page) + page_off + pp_frag_offset_val,
> + page_address(p) + offset, *len);
> page_off += *len;
>
> while (--*num_buf) {
> @@ -948,7 +959,7 @@ static struct page *xdp_linearize_page(struct receive_queue *rq,
> goto err_buf;
> }
>
> - memcpy(page_address(page) + page_off,
> + memcpy(page_address(page) + page_off + pp_frag_offset_val,
> page_address(p) + off, buflen);
> page_off += buflen;
> virtnet_put_page(rq, p);
> @@ -1029,7 +1040,7 @@ static struct sk_buff *receive_small_xdp(struct net_device *dev,
> SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
> xdp_page = xdp_linearize_page(rq, &num_buf, page,
> offset, header_offset,
> - &tlen);
> + &tlen, NULL);
> if (!xdp_page)
> goto err_xdp;
>
> @@ -1323,6 +1334,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> unsigned int headroom = mergeable_ctx_to_headroom(ctx);
> struct page *xdp_page;
> unsigned int xdp_room;
> + unsigned int page_frag_offset = 0;
>
> /* Transient failure which in theory could occur if
> * in-flight packets from before XDP was enabled reach
> @@ -1356,7 +1368,8 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> xdp_page = xdp_linearize_page(rq, num_buf,
> *page, offset,
> VIRTIO_XDP_HEADROOM,
> - len);
> + len,
> + &page_frag_offset);
> if (!xdp_page)
> return NULL;
> } else {
> @@ -1366,14 +1379,19 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
> return NULL;
>
> if (rq->page_pool)
> - xdp_page = page_pool_dev_alloc_pages(rq->page_pool);
> + if (rq->page_pool->p.flags & PP_FLAG_PAGE_FRAG)
> + xdp_page = page_pool_dev_alloc_frag(rq->page_pool,
> + &page_frag_offset, PAGE_SIZE);
> + else
> + xdp_page = page_pool_dev_alloc_pages(rq->page_pool);
> else
> xdp_page = alloc_page(GFP_ATOMIC);
> +
> if (!xdp_page)
> return NULL;
>
> - memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM,
> - page_address(*page) + offset, *len);
> + memcpy(page_address(xdp_page) + VIRTIO_XDP_HEADROOM +
> + page_frag_offset, page_address(*page) + offset, *len);
> }
>
> *frame_sz = PAGE_SIZE;
> @@ -1382,7 +1400,7 @@ static void *mergeable_xdp_get_buf(struct virtnet_info *vi,
>
> *page = xdp_page;
>
> - return page_address(*page) + VIRTIO_XDP_HEADROOM;
> + return page_address(*page) + VIRTIO_XDP_HEADROOM + page_frag_offset;
> }
>
> static struct sk_buff *receive_mergeable_xdp(struct net_device *dev,
> @@ -1762,6 +1780,7 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> void *ctx;
> int err;
> unsigned int len, hole;
> + unsigned int pp_frag_offset;
>
> /* Extra tailroom is needed to satisfy XDP's assumption. This
> * means rx frags coalescing won't work, but consider we've
> @@ -1769,13 +1788,29 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
> */
> len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
> if (rq->page_pool) {
> - struct page *page;
> + if (rq->page_pool->p.flags & PP_FLAG_PAGE_FRAG) {
> + if (unlikely(!page_pool_dev_alloc_frag(rq->page_pool,
> + &pp_frag_offset, len + room)))
> + return -ENOMEM;
> + buf = (char *)page_address(rq->page_pool->frag_page) +
> + pp_frag_offset;
> + buf += headroom; /* advance address leaving hole at front of pkt */
> + hole = (PAGE_SIZE << rq->page_pool->p.order)
> + - rq->page_pool->frag_offset;
> + if (hole < len + room) {
> + if (!headroom)
> + len += hole;
> + rq->page_pool->frag_offset += hole;
> + }
> + } else {
> + struct page *page;
>
> - 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 */
> + 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)))
> return -ENOMEM;
> @@ -3800,13 +3835,16 @@ 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,
> + .order = page_pool_frag ? SKB_FRAG_PAGE_ORDER : 0,
> .pool_size = rq->vq->num_max,
> .nid = dev_to_node(vdev->dev.parent),
> .dev = vdev->dev.parent,
> .offset = 0,
> };
>
> + if (page_pool_frag)
> + pp_params.flags |= PP_FLAG_PAGE_FRAG;
> +
> rq->page_pool = page_pool_create(&pp_params);
> if (IS_ERR(rq->page_pool)) {
> dev_warn(&vdev->dev, "page pool creation failed: %ld\n",
> --
> 2.31.1
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