[bpf-next V4 PATCH 6/8] xdp: change ndo_xdp_xmit API to support bulking

Jesper Dangaard Brouer
2018-05-18T13:35:04Z

This patch change the API for ndo_xdp_xmit to support bulking
xdp_frames.

When kernel is compiled with CONFIG_RETPOLINE, XDP sees a huge slowdown.
Most of the slowdown is caused by DMA API indirect function calls, but
also the net_device->ndo_xdp_xmit() call.

Benchmarked patch with CONFIG_RETPOLINE, using xdp_redirect_map with
single flow/core test (CPU E5-1650 v4 @ 3.60GHz), showed
performance improved:
for driver ixgbe: 6,042,682 pps -> 6,853,768 pps = +811,086 pps
for driver i40e : 6,187,169 pps -> 6,724,519 pps = +537,350 pps

With frames avail as a bulk inside the driver ndo_xdp_xmit call,
further optimizations are possible, like bulk DMA-mapping for TX.

Testing without CONFIG_RETPOLINE show the same performance for
physical NIC drivers.

The virtual NIC driver tun sees a huge performance boost, as it can
avoid doing per frame producer locking, but instead amortize the
locking cost over the bulk.

V2: Fix compile errors reported by kbuild test robot <lkp@intel.com>
V4: Isolated ndo, driver changes and callers.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
---
drivers/net/ethernet/intel/i40e/i40e_txrx.c | 26 +++++++---
drivers/net/ethernet/intel/i40e/i40e_txrx.h | 2 -
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 21 ++++++--
drivers/net/tun.c | 37 +++++++++-----
drivers/net/virtio_net.c | 66 +++++++++++++++++++------
include/linux/netdevice.h | 14 +++--
kernel/bpf/devmap.c | 31 ++++++++----
net/core/filter.c | 8 ++-
8 files changed, 141 insertions(+), 64 deletions(-)

diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.c b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
index 5efa68de935b..9b698c5acd05 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.c
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.c
@@ -3664,14 +3664,19 @@ netdev_tx_t i40e_lan_xmit_frame(struct sk_buff *skb, struct net_device *netdev)
* @dev: netdev
* @xdp: XDP buffer
*
- * Returns Zero if sent, else an error code
+ * Returns number of frames successfully sent. Frames that fail are
+ * free'ed via XDP return API.
+ *
+ * For error cases, a negative errno code is returned and no-frames
+ * are transmitted (caller must handle freeing frames).
**/
-int i40e_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
+int i40e_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frames)
{
struct i40e_netdev_priv *np = netdev_priv(dev);
unsigned int queue_index = smp_processor_id();
struct i40e_vsi *vsi = np->vsi;
- int err;
+ int drops = 0;
+ int i;

if (test_bit(__I40E_VSI_DOWN, vsi->state))
return -ENETDOWN;
@@ -3679,11 +3684,18 @@ int i40e_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
if (!i40e_enabled_xdp_vsi(vsi) || queue_index >= vsi->num_queue_pairs)
return -ENXIO;

- err = i40e_xmit_xdp_ring(xdpf, vsi->xdp_rings[queue_index]);
- if (err != I40E_XDP_TX)
- return -ENOSPC;
+ for (i = 0; i < n; i++) {
+ struct xdp_frame *xdpf = frames[i];
+ int err;

- return 0;
+ err = i40e_xmit_xdp_ring(xdpf, vsi->xdp_rings[queue_index]);
+ if (err != I40E_XDP_TX) {
+ xdp_return_frame_rx_napi(xdpf);
+ drops++;
+ }
+ }
+
+ return n - drops;
}

/**
diff --git a/drivers/net/ethernet/intel/i40e/i40e_txrx.h b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
index fdd2c55f03a6..eb8804b3d7b6 100644
--- a/drivers/net/ethernet/intel/i40e/i40e_txrx.h
+++ b/drivers/net/ethernet/intel/i40e/i40e_txrx.h
@@ -487,7 +487,7 @@ u32 i40e_get_tx_pending(struct i40e_ring *ring, bool in_sw);
void i40e_detect_recover_hung(struct i40e_vsi *vsi);
int __i40e_maybe_stop_tx(struct i40e_ring *tx_ring, int size);
bool __i40e_chk_linearize(struct sk_buff *skb);
-int i40e_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf);
+int i40e_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frames);
void i40e_xdp_flush(struct net_device *dev);

/**
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index 6652b201df5b..9645619f7729 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -10017,11 +10017,13 @@ static int ixgbe_xdp(struct net_device *dev, struct netdev_bpf *xdp)
}
}

-static int ixgbe_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
+static int ixgbe_xdp_xmit(struct net_device *dev, int n,
+ struct xdp_frame **frames)
{
struct ixgbe_adapter *adapter = netdev_priv(dev);
struct ixgbe_ring *ring;
- int err;
+ int drops = 0;
+ int i;

if (unlikely(test_bit(__IXGBE_DOWN, &adapter->state)))
return -ENETDOWN;
@@ -10033,11 +10035,18 @@ static int ixgbe_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
if (unlikely(!ring))
return -ENXIO;

- err = ixgbe_xmit_xdp_ring(adapter, xdpf);
- if (err != IXGBE_XDP_TX)
- return -ENOSPC;
+ for (i = 0; i < n; i++) {
+ struct xdp_frame *xdpf = frames[i];
+ int err;

- return 0;
+ err = ixgbe_xmit_xdp_ring(adapter, xdpf);
+ if (err != IXGBE_XDP_TX) {
+ xdp_return_frame_rx_napi(xdpf);
+ drops++;
+ }
+ }
+
+ return n - drops;
}

static void ixgbe_xdp_flush(struct net_device *dev)
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index 44d4f3d25350..d3dcfcb1c4b3 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -70,6 +70,7 @@
#include <net/netns/generic.h>
#include <net/rtnetlink.h>
#include <net/sock.h>
+#include <net/xdp.h>
#include <linux/seq_file.h>
#include <linux/uio.h>
#include <linux/skb_array.h>
@@ -1290,34 +1291,44 @@ static const struct net_device_ops tun_netdev_ops = {
.ndo_get_stats64 = tun_net_get_stats64,
};

-static int tun_xdp_xmit(struct net_device *dev, struct xdp_frame *frame)
+static int tun_xdp_xmit(struct net_device *dev, int n, struct xdp_frame **frames)
{
struct tun_struct *tun = netdev_priv(dev);
struct tun_file *tfile;
u32 numqueues;
- int ret = 0;
+ int drops = 0;
+ int cnt = n;
+ int i;

rcu_read_lock();

numqueues = READ_ONCE(tun->numqueues);
if (!numqueues) {
- ret = -ENOSPC;
- goto out;
+ rcu_read_unlock();
+ return -ENXIO; /* Caller will free/return all frames */
}

tfile = rcu_dereference(tun->tfiles[smp_processor_id() %
numqueues]);
- /* Encode the XDP flag into lowest bit for consumer to differ
- * XDP buffer from sk_buff.
- */
- if (ptr_ring_produce(&tfile->tx_ring, tun_xdp_to_ptr(frame))) {
- this_cpu_inc(tun->pcpu_stats->tx_dropped);
- ret = -ENOSPC;
+
+ spin_lock(&tfile->tx_ring.producer_lock);
+ for (i = 0; i < n; i++) {
+ struct xdp_frame *xdp = frames[i];
+ /* Encode the XDP flag into lowest bit for consumer to differ
+ * XDP buffer from sk_buff.
+ */
+ void *frame = tun_xdp_to_ptr(xdp);
+
+ if (__ptr_ring_produce(&tfile->tx_ring, frame)) {
+ this_cpu_inc(tun->pcpu_stats->tx_dropped);
+ xdp_return_frame_rx_napi(xdp);
+ drops++;
+ }
}
+ spin_unlock(&tfile->tx_ring.producer_lock);

-out:
rcu_read_unlock();
- return ret;
+ return cnt - drops;
}

static int tun_xdp_tx(struct net_device *dev, struct xdp_buff *xdp)
@@ -1327,7 +1338,7 @@ static int tun_xdp_tx(struct net_device *dev, struct xdp_buff *xdp)
if (unlikely(!frame))
return -EOVERFLOW;

- return tun_xdp_xmit(dev, frame);
+ return tun_xdp_xmit(dev, 1, &frame);
}

static void tun_xdp_flush(struct net_device *dev)
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index f34794a76c4d..39a0783d1cde 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -419,23 +419,13 @@ static void virtnet_xdp_flush(struct net_device *dev)
virtqueue_kick(sq->vq);
}

-static int __virtnet_xdp_xmit(struct virtnet_info *vi,
- struct xdp_frame *xdpf)
+static int __virtnet_xdp_xmit_one(struct virtnet_info *vi,
+ struct send_queue *sq,
+ struct xdp_frame *xdpf)
{
struct virtio_net_hdr_mrg_rxbuf *hdr;
- struct xdp_frame *xdpf_sent;
- struct send_queue *sq;
- unsigned int len;
- unsigned int qp;
int err;

- qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
- sq = &vi->sq[qp];
-
- /* Free up any pending old buffers before queueing new ones. */
- while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
- xdp_return_frame(xdpf_sent);
-
/* virtqueue want to use data area in-front of packet */
if (unlikely(xdpf->metasize > 0))
return -EOPNOTSUPP;
@@ -459,11 +449,40 @@ static int __virtnet_xdp_xmit(struct virtnet_info *vi,
return 0;
}

-static int virtnet_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
+static int __virtnet_xdp_tx_xmit(struct virtnet_info *vi,
+ struct xdp_frame *xdpf)
+{
+ struct xdp_frame *xdpf_sent;
+ struct send_queue *sq;
+ unsigned int len;
+ unsigned int qp;
+
+ qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
+ sq = &vi->sq[qp];
+
+ /* Free up any pending old buffers before queueing new ones. */
+ while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
+ xdp_return_frame(xdpf_sent);
+
+ return __virtnet_xdp_xmit_one(vi, sq, xdpf);
+}
+
+static int virtnet_xdp_xmit(struct net_device *dev,
+ int n, struct xdp_frame **frames)
{
struct virtnet_info *vi = netdev_priv(dev);
struct receive_queue *rq = vi->rq;
+ struct xdp_frame *xdpf_sent;
struct bpf_prog *xdp_prog;
+ struct send_queue *sq;
+ unsigned int len;
+ unsigned int qp;
+ int drops = 0;
+ int err;
+ int i;
+
+ qp = vi->curr_queue_pairs - vi->xdp_queue_pairs + smp_processor_id();
+ sq = &vi->sq[qp];

/* Only allow ndo_xdp_xmit if XDP is loaded on dev, as this
* indicate XDP resources have been successfully allocated.
@@ -472,7 +491,20 @@ static int virtnet_xdp_xmit(struct net_device *dev, struct xdp_frame *xdpf)
if (!xdp_prog)
return -ENXIO;

- return __virtnet_xdp_xmit(vi, xdpf);
+ /* Free up any pending old buffers before queueing new ones. */
+ while ((xdpf_sent = virtqueue_get_buf(sq->vq, &len)) != NULL)
+ xdp_return_frame(xdpf_sent);
+
+ for (i = 0; i < n; i++) {
+ struct xdp_frame *xdpf = frames[i];
+
+ err = __virtnet_xdp_xmit_one(vi, sq, xdpf);
+ if (err) {
+ xdp_return_frame_rx_napi(xdpf);
+ drops++;
+ }
+ }
+ return n - drops;
}

static unsigned int virtnet_get_headroom(struct virtnet_info *vi)
@@ -616,7 +648,7 @@ static struct sk_buff *receive_small(struct net_device *dev,
xdpf = convert_to_xdp_frame(&xdp);
if (unlikely(!xdpf))
goto err_xdp;
- err = __virtnet_xdp_xmit(vi, xdpf);
+ err = __virtnet_xdp_tx_xmit(vi, xdpf);
if (unlikely(err)) {
trace_xdp_exception(vi->dev, xdp_prog, act);
goto err_xdp;
@@ -779,7 +811,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
xdpf = convert_to_xdp_frame(&xdp);
if (unlikely(!xdpf))
goto err_xdp;
- err = __virtnet_xdp_xmit(vi, xdpf);
+ err = __virtnet_xdp_tx_xmit(vi, xdpf);
if (unlikely(err)) {
trace_xdp_exception(vi->dev, xdp_prog, act);
if (unlikely(xdp_page != page))
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 03ed492c4e14..debdb6286170 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1185,9 +1185,13 @@ struct dev_ifalias {
* This function is used to set or query state related to XDP on the
* netdevice and manage BPF offload. See definition of
* enum bpf_netdev_command for details.
- * int (*ndo_xdp_xmit)(struct net_device *dev, struct xdp_frame *xdp);
- * This function is used to submit a XDP packet for transmit on a
- * netdevice.
+ * int (*ndo_xdp_xmit)(struct net_device *dev, int n, struct xdp_frame **xdp);
+ * This function is used to submit @n XDP packets for transmit on a
+ * netdevice. Returns number of frames successfully transmitted, frames
+ * that got dropped are freed/returned via xdp_return_frame().
+ * Returns negative number, means general error invoking ndo, meaning
+ * no frames were xmit'ed and core-caller will free all frames.
+ * TODO: Consider add flag to allow sending flush operation.
* void (*ndo_xdp_flush)(struct net_device *dev);
* This function is used to inform the driver to flush a particular
* xdp tx queue. Must be called on same CPU as xdp_xmit.
@@ -1375,8 +1379,8 @@ struct net_device_ops {
int needed_headroom);
int (*ndo_bpf)(struct net_device *dev,
struct netdev_bpf *bpf);
- int (*ndo_xdp_xmit)(struct net_device *dev,
- struct xdp_frame *xdp);
+ int (*ndo_xdp_xmit)(struct net_device *dev, int n,
+ struct xdp_frame **xdp);
void (*ndo_xdp_flush)(struct net_device *dev);
};

diff --git a/kernel/bpf/devmap.c b/kernel/bpf/devmap.c
index 6f84100723b0..1317629662ae 100644
--- a/kernel/bpf/devmap.c
+++ b/kernel/bpf/devmap.c
@@ -222,7 +222,7 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
struct xdp_bulk_queue *bq)
{
struct net_device *dev = obj->dev;
- int sent = 0, drops = 0;
+ int sent = 0, drops = 0, err = 0;
int i;

if (unlikely(!bq->count))
@@ -234,23 +234,32 @@ static int bq_xmit_all(struct bpf_dtab_netdev *obj,
prefetch(xdpf);
}

- for (i = 0; i < bq->count; i++) {
- struct xdp_frame *xdpf = bq->q[i];
- int err;
-
- err = dev->netdev_ops->ndo_xdp_xmit(dev, xdpf);
- if (err) {
- drops++;
- xdp_return_frame(xdpf);
- }
- sent++;
+ sent = dev->netdev_ops->ndo_xdp_xmit(dev, bq->count, bq->q);
+ if (sent < 0) {
+ err = sent;
+ sent = 0;
+ goto error;
}
+ drops = bq->count - sent;
+out:
bq->count = 0;

trace_xdp_devmap_xmit(&obj->dtab->map, obj->bit,
sent, drops, bq->dev_rx, dev);
bq->dev_rx = NULL;
return 0;
+error:
+ /* If ndo_xdp_xmit fails with an errno, no frames have been
+ * xmit'ed and it's our responsibility to them free all.
+ */
+ for (i = 0; i < bq->count; i++) {
+ struct xdp_frame *xdpf = bq->q[i];
+
+ /* RX path under NAPI protection, can return frames faster */
+ xdp_return_frame_rx_napi(xdpf);
+ drops++;
+ }
+ goto out;
}

/* __dev_map_flush is called from xdp_do_flush_map() which _must_ be signaled
diff --git a/net/core/filter.c b/net/core/filter.c
index 4a93423cc5ea..19504b7f4959 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -3035,7 +3035,7 @@ static int __bpf_tx_xdp(struct net_device *dev,
u32 index)
{
struct xdp_frame *xdpf;
- int err;
+ int sent;

if (!dev->netdev_ops->ndo_xdp_xmit) {
return -EOPNOTSUPP;
@@ -3045,9 +3045,9 @@ static int __bpf_tx_xdp(struct net_device *dev,
if (unlikely(!xdpf))
return -EOVERFLOW;

- err = dev->netdev_ops->ndo_xdp_xmit(dev, xdpf);
- if (err)
- return err;
+ sent = dev->netdev_ops->ndo_xdp_xmit(dev, 1, &xdpf);
+ if (sent <= 0)
+ return sent;
dev->netdev_ops->ndo_xdp_flush(dev);
return 0;
}