Changing API xdp_return_frame() to take struct xdp_frame as argument,
seems like a natural choice. But there are some subtle performance
details here that needs extra care, which is a deliberate choice.
When de-referencing xdp_frame on a remote CPU during DMA-TX
completion, result in the cache-line is change to "Shared"
state. Later when the page is reused for RX, then this xdp_frame
cache-line is written, which change the state to "Modified".
This situation already happens (naturally) for, virtio_net, tun and
cpumap as the xdp_frame pointer is the queued object. In tun and
cpumap, the ptr_ring is used for efficiently transferring cache-lines
(with pointers) between CPUs. Thus, the only option is to
de-referencing xdp_frame.
It is only the ixgbe driver that had an optimization, in which it can
avoid doing the de-reference of xdp_frame. The driver already have
TX-ring queue, which (in case of remote DMA-TX completion) have to be
transferred between CPUs anyhow. In this data area, we stored a
struct xdp_mem_info and a data pointer, which allowed us to avoid
de-referencing xdp_frame.
To compensate for this, a prefetchw is used for telling the cache
coherency protocol about our access pattern. My benchmarks show that
this prefetchw is enough to compensate the ixgbe driver.
Signed-off-by: Jesper Dangaard Brouer <bro...@redhat.com>
---
drivers/net/ethernet/intel/ixgbe/ixgbe.h | 4 +---
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 17 +++++++++++------
drivers/net/ethernet/mellanox/mlx5/core/en_rx.c | 1 +
drivers/net/tun.c | 4 ++--
drivers/net/virtio_net.c | 2 +-
include/net/xdp.h | 2 +-
kernel/bpf/cpumap.c | 6 +++---
net/core/xdp.c | 4 +++-
8 files changed, 23 insertions(+), 17 deletions(-)
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
index cbc20f199364..dfbc15a45cb4 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe.h
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe.h
@@ -240,8 +240,7 @@ struct ixgbe_tx_buffer {
unsigned long time_stamp;
union {
struct sk_buff *skb;
- /* XDP uses address ptr on irq_clean */
- void *data;
+ struct xdp_frame *xdpf;
};
unsigned int bytecount;
unsigned short gso_segs;
@@ -249,7 +248,6 @@ struct ixgbe_tx_buffer {
DEFINE_DMA_UNMAP_ADDR(dma);
DEFINE_DMA_UNMAP_LEN(len);
u32 tx_flags;
- struct xdp_mem_info xdp_mem;
};
struct ixgbe_rx_buffer {
diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
index ff069597fccf..e6e9b28ecfba 100644
--- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
+++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
@@ -1207,7 +1207,7 @@ static bool ixgbe_clean_tx_irq(struct ixgbe_q_vector
*q_vector,
/* free the skb */
if (ring_is_xdp(tx_ring))
- xdp_return_frame(tx_buffer->data, &tx_buffer->xdp_mem);
+ xdp_return_frame(tx_buffer->xdpf);
else
napi_consume_skb(tx_buffer->skb, napi_budget);
@@ -2376,6 +2376,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector
*q_vector,
xdp.data_hard_start = xdp.data -
ixgbe_rx_offset(rx_ring);
xdp.data_end = xdp.data + size;
+ prefetchw(xdp.data_hard_start); /* xdp_frame write */
skb = ixgbe_run_xdp(adapter, rx_ring, &xdp);
}
@@ -5787,7 +5788,7 @@ static void ixgbe_clean_tx_ring(struct ixgbe_ring
*tx_ring)
/* Free all the Tx ring sk_buffs */
if (ring_is_xdp(tx_ring))
- xdp_return_frame(tx_buffer->data, &tx_buffer->xdp_mem);
+ xdp_return_frame(tx_buffer->xdpf);
else
dev_kfree_skb_any(tx_buffer->skb);
@@ -8333,16 +8334,21 @@ static int ixgbe_xmit_xdp_ring(struct ixgbe_adapter
*adapter,
struct ixgbe_ring *ring = adapter->xdp_ring[smp_processor_id()];
struct ixgbe_tx_buffer *tx_buffer;
union ixgbe_adv_tx_desc *tx_desc;
+ struct xdp_frame *xdpf;
u32 len, cmd_type;
dma_addr_t dma;
u16 i;
- len = xdp->data_end - xdp->data;
+ xdpf = convert_to_xdp_frame(xdp);
+ if (unlikely(!xdpf))
+ return -EOVERFLOW;
+
+ len = xdpf->len;
if (unlikely(!ixgbe_desc_unused(ring)))
return IXGBE_XDP_CONSUMED;
- dma = dma_map_single(ring->dev, xdp->data, len, DMA_TO_DEVICE);
+ dma = dma_map_single(ring->dev, xdpf->data, len, DMA_TO_DEVICE);
if (dma_mapping_error(ring->dev, dma))
return IXGBE_XDP_CONSUMED;
@@ -8357,8 +8363,7 @@ static int ixgbe_xmit_xdp_ring(struct ixgbe_adapter
*adapter,
dma_unmap_len_set(tx_buffer, len, len);
dma_unmap_addr_set(tx_buffer, dma, dma);
- tx_buffer->data = xdp->data;
- tx_buffer->xdp_mem = xdp->rxq->mem;
+ tx_buffer->xdpf = xdpf;
tx_desc->read.buffer_addr = cpu_to_le64(dma);
diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
index 2ac78b88fc3d..00b9b13d9fea 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_rx.c
@@ -896,6 +896,7 @@ struct sk_buff *skb_from_cqe(struct mlx5e_rq *rq, struct
mlx5_cqe64 *cqe,
di->addr + wi->offset,
0, frag_size,
DMA_FROM_DEVICE);
+ prefetchw(va); /* xdp_frame data area */
prefetch(data);
wi->offset += frag_size;
diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index cd046cf31b77..fedf01ca3e51 100644
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -663,7 +663,7 @@ static void tun_ptr_free(void *ptr)
if (tun_is_xdp_frame(ptr)) {
struct xdp_frame *xdpf = tun_ptr_to_xdp(ptr);
- xdp_return_frame(xdpf->data, &xdpf->mem);
+ xdp_return_frame(xdpf);
} else {
__skb_array_destroy_skb(ptr);
}
@@ -2189,7 +2189,7 @@ static ssize_t tun_do_read(struct tun_struct *tun, struct
tun_file *tfile,
struct xdp_frame *xdpf = tun_ptr_to_xdp(ptr);
ret = tun_put_user_xdp(tun, tfile, xdpf, to);
- xdp_return_frame(xdpf->data, &xdpf->mem);
+ xdp_return_frame(xdpf);
} else {
struct sk_buff *skb = ptr;
diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 6c4220450506..9fdb70fe74fe 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -430,7 +430,7 @@ static bool __virtnet_xdp_xmit(struct virtnet_info *vi,
/* 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->data, &xdpf_sent->mem);
+ xdp_return_frame(xdpf_sent);
xdpf = convert_to_xdp_frame(xdp);
if (unlikely(!xdpf))
diff --git a/include/net/xdp.h b/include/net/xdp.h
index 26eb645c699a..ca023a1fd95b 100644
--- a/include/net/xdp.h
+++ b/include/net/xdp.h
@@ -106,7 +106,7 @@ struct xdp_frame *convert_to_xdp_frame(struct xdp_buff *xdp)
return xdp_frame;
}
-void xdp_return_frame(void *data, struct xdp_mem_info *mem);
+void xdp_return_frame(struct xdp_frame *xdpf);
int xdp_rxq_info_reg(struct xdp_rxq_info *xdp_rxq,
struct net_device *dev, u32 queue_index);
diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
index bcdc4dea5ce7..c95b04ec103e 100644
--- a/kernel/bpf/cpumap.c
+++ b/kernel/bpf/cpumap.c
@@ -219,7 +219,7 @@ static void __cpu_map_ring_cleanup(struct ptr_ring *ring)
while ((xdpf = ptr_ring_consume(ring)))
if (WARN_ON_ONCE(xdpf))
- xdp_return_frame(xdpf->data, &xdpf->mem);
+ xdp_return_frame(xdpf);
}
static void put_cpu_map_entry(struct bpf_cpu_map_entry *rcpu)
@@ -275,7 +275,7 @@ static int cpu_map_kthread_run(void *data)
skb = cpu_map_build_skb(rcpu, xdpf);
if (!skb) {
- xdp_return_frame(xdpf->data, &xdpf->mem);
+ xdp_return_frame(xdpf);
continue;
}
@@ -578,7 +578,7 @@ static int bq_flush_to_queue(struct bpf_cpu_map_entry *rcpu,
err = __ptr_ring_produce(q, xdpf);
if (err) {
drops++;
- xdp_return_frame(xdpf->data, &xdpf->mem);
+ xdp_return_frame(xdpf);
}
processed++;
}
diff --git a/net/core/xdp.c b/net/core/xdp.c
index fe8e87abc266..6ed3d73a73be 100644
--- a/net/core/xdp.c
+++ b/net/core/xdp.c
@@ -294,9 +294,11 @@ int xdp_rxq_info_reg_mem_model(struct xdp_rxq_info
*xdp_rxq,
}
EXPORT_SYMBOL_GPL(xdp_rxq_info_reg_mem_model);
-void xdp_return_frame(void *data, struct xdp_mem_info *mem)
+void xdp_return_frame(struct xdp_frame *xdpf)
{
struct xdp_mem_allocator *xa = NULL;
+ struct xdp_mem_info *mem = &xdpf->mem;
+ void *data = xdpf->data;
rcu_read_lock();
if (mem->id)
