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Message-ID: <20e27fa0-c7c3-0cc3-bd27-19d1fe9b7717@redhat.com>
Date: Mon, 18 Jan 2021 17:10:24 +0800
From: Jason Wang <jasowang@...hat.com>
To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org
Cc: "Michael S. Tsirkin" <mst@...hat.com>,
"David S. Miller" <davem@...emloft.net>,
Jakub Kicinski <kuba@...nel.org>,
Björn Töpel <bjorn.topel@...el.com>,
Magnus Karlsson <magnus.karlsson@...el.com>,
Jonathan Lemon <jonathan.lemon@...il.com>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Jesper Dangaard Brouer <hawk@...nel.org>,
John Fastabend <john.fastabend@...il.com>,
Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <kafai@...com>,
Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
KP Singh <kpsingh@...nel.org>,
virtualization@...ts.linux-foundation.org, bpf@...r.kernel.org
Subject: Re: [PATCH net-next v2 5/7] virtio-net, xsk: realize the function of
xsk packet sending
On 2021/1/16 上午10:59, Xuan Zhuo wrote:
> virtnet_xsk_run will be called in the tx interrupt handling function
> virtnet_poll_tx.
>
> The sending process gets desc from the xsk tx queue, and assembles it to
> send the data.
>
> Compared with other drivers, a special place is that the page of the
> data in xsk is used here instead of the dma address. Because the virtio
> interface does not use the dma address.
>
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
> drivers/net/virtio_net.c | 200 ++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 197 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index a62d456..42aa9ad 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -119,6 +119,8 @@ struct virtnet_xsk_hdr {
> u32 len;
> };
>
> +#define VIRTNET_STATE_XSK_WAKEUP 1
> +
> #define VIRTNET_SQ_STAT(m) offsetof(struct virtnet_sq_stats, m)
> #define VIRTNET_RQ_STAT(m) offsetof(struct virtnet_rq_stats, m)
>
> @@ -163,9 +165,12 @@ struct send_queue {
> struct xsk_buff_pool __rcu *pool;
> struct virtnet_xsk_hdr __rcu *hdr;
>
> + unsigned long state;
> u64 hdr_con;
> u64 hdr_pro;
> u64 hdr_n;
> + struct xdp_desc last_desc;
> + bool wait_slot;
> } xsk;
> };
>
> @@ -284,6 +289,8 @@ static void __free_old_xmit_ptr(struct send_queue *sq, bool in_napi,
> bool xsk_wakeup,
> unsigned int *_packets, unsigned int *_bytes);
> static void free_old_xmit_skbs(struct send_queue *sq, bool in_napi);
> +static int virtnet_xsk_run(struct send_queue *sq,
> + struct xsk_buff_pool *pool, int budget);
>
> static bool is_xdp_frame(void *ptr)
> {
> @@ -1590,6 +1597,8 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
> struct virtnet_info *vi = sq->vq->vdev->priv;
> unsigned int index = vq2txq(sq->vq);
> struct netdev_queue *txq;
> + struct xsk_buff_pool *pool;
> + int work = 0;
>
> if (unlikely(is_xdp_raw_buffer_queue(vi, index))) {
> /* We don't need to enable cb for XDP */
> @@ -1599,15 +1608,26 @@ static int virtnet_poll_tx(struct napi_struct *napi, int budget)
>
> txq = netdev_get_tx_queue(vi->dev, index);
> __netif_tx_lock(txq, raw_smp_processor_id());
> - free_old_xmit_skbs(sq, true);
> +
> + rcu_read_lock();
> + pool = rcu_dereference(sq->xsk.pool);
> + if (pool) {
> + work = virtnet_xsk_run(sq, pool, budget);
> + rcu_read_unlock();
> + } else {
> + rcu_read_unlock();
> + free_old_xmit_skbs(sq, true);
> + }
> +
> __netif_tx_unlock(txq);
>
> - virtqueue_napi_complete(napi, sq->vq, 0);
> + if (work < budget)
> + virtqueue_napi_complete(napi, sq->vq, 0);
>
> if (sq->vq->num_free >= 2 + MAX_SKB_FRAGS)
> netif_tx_wake_queue(txq);
>
> - return 0;
> + return work;
> }
>
> static int xmit_skb(struct send_queue *sq, struct sk_buff *skb)
> @@ -2647,6 +2667,180 @@ static int virtnet_xdp(struct net_device *dev, struct netdev_bpf *xdp)
> }
> }
>
> +static int virtnet_xsk_xmit(struct send_queue *sq, struct xsk_buff_pool *pool,
> + struct xdp_desc *desc)
> +{
> + struct virtnet_info *vi = sq->vq->vdev->priv;
> + void *data, *ptr;
> + struct page *page;
> + struct virtnet_xsk_hdr *xskhdr;
> + u32 idx, offset, n, i, copy, copied;
> + u64 addr;
> + int err, m;
> +
> + addr = desc->addr;
> +
> + data = xsk_buff_raw_get_data(pool, addr);
> + offset = offset_in_page(data);
> +
> + /* one for hdr, one for the first page */
> + n = 2;
> + m = desc->len - (PAGE_SIZE - offset);
> + if (m > 0) {
> + n += m >> PAGE_SHIFT;
> + if (m & PAGE_MASK)
> + ++n;
> +
> + n = min_t(u32, n, ARRAY_SIZE(sq->sg));
> + }
> +
> + idx = sq->xsk.hdr_con % sq->xsk.hdr_n;
I don't understand the reason of the hdr array. It looks to me all of
them are zero and read only from device.
Any reason for not reusing a single hdr for all xdp descriptors? Or
maybe it's time to introduce VIRTIO_NET_F_NO_HDR.
> + xskhdr = &sq->xsk.hdr[idx];
> +
> + /* xskhdr->hdr has been memset to zero, so not need to clear again */
> +
> + sg_init_table(sq->sg, n);
> + sg_set_buf(sq->sg, &xskhdr->hdr, vi->hdr_len);
> +
> + copied = 0;
> + for (i = 1; i < n; ++i) {
> + copy = min_t(int, desc->len - copied, PAGE_SIZE - offset);
> +
> + page = xsk_buff_raw_get_page(pool, addr + copied);
> +
> + sg_set_page(sq->sg + i, page, copy, offset);
> + copied += copy;
> + if (offset)
> + offset = 0;
> + }
It looks to me we need to terminate the sg:
**
* virtqueue_add_outbuf - expose output buffers to other end
* @vq: the struct virtqueue we're talking about.
* @sg: scatterlist (must be well-formed and terminated!)
> +
> + xskhdr->len = desc->len;
> + ptr = xdp_to_ptr(&xskhdr->type);
> +
> + err = virtqueue_add_outbuf(sq->vq, sq->sg, n, ptr, GFP_ATOMIC);
> + if (unlikely(err))
> + sq->xsk.last_desc = *desc;
> + else
> + sq->xsk.hdr_con++;
> +
> + return err;
> +}
> +
> +static bool virtnet_xsk_dev_is_full(struct send_queue *sq)
> +{
> + if (sq->vq->num_free < 2 + MAX_SKB_FRAGS)
> + return true;
> +
> + if (sq->xsk.hdr_con == sq->xsk.hdr_pro)
> + return true;
Can we really reach here?
> +
> + return false;
> +}
> +
> +static int virtnet_xsk_xmit_zc(struct send_queue *sq,
> + struct xsk_buff_pool *pool, unsigned int budget)
> +{
> + struct xdp_desc desc;
> + int err, packet = 0;
> + int ret = -EAGAIN;
> +
> + if (sq->xsk.last_desc.addr) {
> + err = virtnet_xsk_xmit(sq, pool, &sq->xsk.last_desc);
> + if (unlikely(err))
> + return -EBUSY;
> +
> + ++packet;
> + sq->xsk.last_desc.addr = 0;
> + }
> +
> + while (budget-- > 0) {
> + if (virtnet_xsk_dev_is_full(sq)) {
> + ret = -EBUSY;
> + break;
> + }
It looks to me we will always hit this if userspace is fast. E.g we
don't kick until the virtqueue is full ...
> +
> + if (!xsk_tx_peek_desc(pool, &desc)) {
> + /* done */
> + ret = 0;
> + break;
> + }
> +
> + err = virtnet_xsk_xmit(sq, pool, &desc);
> + if (unlikely(err)) {
> + ret = -EBUSY;
> + break;
> + }
> +
> + ++packet;
> + }
> +
> + if (packet) {
> + xsk_tx_release(pool);
> +
> + if (virtqueue_kick_prepare(sq->vq) && virtqueue_notify(sq->vq)) {
> + u64_stats_update_begin(&sq->stats.syncp);
> + sq->stats.kicks++;
> + u64_stats_update_end(&sq->stats.syncp);
> + }
> + }
> +
> + return ret;
> +}
> +
> +static int virtnet_xsk_run(struct send_queue *sq,
> + struct xsk_buff_pool *pool, int budget)
> +{
> + int err, ret = 0;
> + unsigned int _packets = 0;
> + unsigned int _bytes = 0;
> +
> + sq->xsk.wait_slot = false;
> +
> + __free_old_xmit_ptr(sq, true, false, &_packets, &_bytes);
> +
> + err = virtnet_xsk_xmit_zc(sq, pool, xsk_budget);
> + if (!err) {
> + struct xdp_desc desc;
> +
> + clear_bit(VIRTNET_STATE_XSK_WAKEUP, &sq->xsk.state);
> + xsk_set_tx_need_wakeup(pool);
> +
> + /* Race breaker. If new is coming after last xmit
> + * but before flag change
> + */
> +
> + if (!xsk_tx_peek_desc(pool, &desc))
> + goto end;
> +
> + set_bit(VIRTNET_STATE_XSK_WAKEUP, &sq->xsk.state);
> + xsk_clear_tx_need_wakeup(pool);
How memory ordering is going to work here? Or we don't need to care
about that?
> +
> + sq->xsk.last_desc = desc;
> + ret = budget;
> + goto end;
> + }
> +
> + xsk_clear_tx_need_wakeup(pool);
> +
> + if (err == -EAGAIN) {
> + ret = budget;
> + goto end;
> + }
> +
> + __free_old_xmit_ptr(sq, true, false, &_packets, &_bytes);
> +
> + if (!virtnet_xsk_dev_is_full(sq)) {
> + ret = budget;
> + goto end;
> + }
> +
> + sq->xsk.wait_slot = true;
> +
> + virtnet_sq_stop_check(sq, true);
> +end:
> + return ret;
> +}
> +
> static int virtnet_get_phys_port_name(struct net_device *dev, char *buf,
> size_t len)
> {
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