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Message-ID: <20210118065907-mutt-send-email-mst@kernel.org>
Date: Mon, 18 Jan 2021 07:27:18 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Jason Wang <jasowang@...hat.com>
Cc: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, netdev@...r.kernel.org,
"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 Mon, Jan 18, 2021 at 05:10:24PM +0800, Jason Wang wrote:
>
> 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;
> > };
Please add documentation about the new fields/defines, how are they
accessed, what locking/ordering is in place.
> > @@ -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.
I'm not sure it's worth it, since
- xdp can be enabled/disabled dynamically
- there's intent to add offload support to xdp
>
> > + 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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