[RFC: DMA_PMD 18/22] net/gve: Use DMA_PMD memory for tx header bounce buffers
From: Luigi Rizzo
Date: Sat Oct 03 2026 - 17:34:24 EST
When dev->dma_pmd_tx_hdrs is enabled, allocate a MAX_TCP_HEADER
bounce buffer per TX slot/packet out of the DMA_PMD arena in raw-addressing
mode (both GQI and DQO). When skb_headlen(skb) <= MAX_TCP_HEADER, the
linear portion is copied into the pre-mapped bounce buffer instead of
calling dma_map_single()/dma_unmap_single() on every packet.
Signed-off-by: Luigi Rizzo <lrizzo@xxxxxxxxxx>
---
drivers/net/ethernet/google/gve/gve.h | 3 ++
drivers/net/ethernet/google/gve/gve_tx.c | 38 ++++++++++++++---
drivers/net/ethernet/google/gve/gve_tx_dqo.c | 45 +++++++++++++++-----
3 files changed, 69 insertions(+), 17 deletions(-)
diff --git a/drivers/net/ethernet/google/gve/gve.h b/drivers/net/ethernet/google/gve/gve.h
index 11330404f681b..00e438fe05a50 100644
--- a/drivers/net/ethernet/google/gve/gve.h
+++ b/drivers/net/ethernet/google/gve/gve.h
@@ -18,6 +18,7 @@
#include <linux/ptp_clock_kernel.h>
#include <linux/u64_stats_sync.h>
#include <net/page_pool/helpers.h>
+#include <net/tcp.h>
#include <net/xdp.h>
#include "gve_desc.h"
@@ -642,6 +643,8 @@ struct gve_tx_ring {
};
} dqo;
} ____cacheline_aligned;
+ void *tx_hdr_bufs;
+ dma_addr_t tx_hdr_bufs_dma;
struct netdev_queue *netdev_txq;
struct gve_queue_resources *q_resources; /* head and tail pointer idx */
struct device *dev;
diff --git a/drivers/net/ethernet/google/gve/gve_tx.c b/drivers/net/ethernet/google/gve/gve_tx.c
index 79338fd9bf66e..9610b54ef4792 100644
--- a/drivers/net/ethernet/google/gve/gve_tx.c
+++ b/drivers/net/ethernet/google/gve/gve_tx.c
@@ -224,6 +224,11 @@ static void gve_tx_free_ring_gqi(struct gve_priv *priv, struct gve_tx_ring *tx,
u32 slots;
slots = tx->mask + 1;
+ if (tx->tx_hdr_bufs) {
+ dma_free_coherent(hdev, slots * MAX_TCP_HEADER,
+ tx->tx_hdr_bufs, tx->tx_hdr_bufs_dma);
+ tx->tx_hdr_bufs = NULL;
+ }
dma_free_coherent(hdev, sizeof(*tx->q_resources),
tx->q_resources, tx->q_resources_bus);
tx->q_resources = NULL;
@@ -298,6 +303,11 @@ static int gve_tx_alloc_ring_gqi(struct gve_priv *priv,
/* map Tx FIFO */
if (gve_tx_fifo_init(priv, &tx->tx_fifo))
goto abort_with_qpl;
+ } else if (hdev->dma_pmd_tx_hdrs) {
+ tx->tx_hdr_bufs = dma_alloc_coherent(hdev,
+ cfg->ring_size * MAX_TCP_HEADER,
+ &tx->tx_hdr_bufs_dma,
+ GFP_KERNEL);
}
tx->q_resources =
@@ -311,6 +321,12 @@ static int gve_tx_alloc_ring_gqi(struct gve_priv *priv,
return 0;
abort_with_fifo:
+ if (tx->tx_hdr_bufs) {
+ dma_free_coherent(hdev,
+ cfg->ring_size * MAX_TCP_HEADER,
+ tx->tx_hdr_bufs, tx->tx_hdr_bufs_dma);
+ tx->tx_hdr_bufs = NULL;
+ }
if (!tx->raw_addressing)
gve_tx_fifo_release(priv, &tx->tx_fifo);
abort_with_qpl:
@@ -423,6 +439,8 @@ static inline int gve_skb_fifo_bytes_required(struct gve_tx_ring *tx,
#define MAX_TX_DESC_NEEDED (MAX_SKB_FRAGS + 4)
static void gve_tx_unmap_buf(struct device *dev, struct gve_tx_buffer_state *info)
{
+ if (!dma_unmap_len(info, len))
+ return;
if (info->skb) {
dma_unmap_single(dev, dma_unmap_addr(info, dma),
dma_unmap_len(info, len),
@@ -657,13 +675,21 @@ static int gve_tx_add_skb_no_copy(struct gve_priv *priv, struct gve_tx_ring *tx,
info->skb = skb;
- addr = dma_map_single(tx->dev, skb->data, len, DMA_TO_DEVICE);
- if (unlikely(dma_mapping_error(tx->dev, addr))) {
- tx->dma_mapping_error++;
- goto drop;
+ if (tx->tx_hdr_bufs && len <= MAX_TCP_HEADER) {
+ u32 hdr_off = idx * MAX_TCP_HEADER;
+
+ memcpy(tx->tx_hdr_bufs + hdr_off, skb->data, len);
+ addr = tx->tx_hdr_bufs_dma + hdr_off;
+ dma_unmap_len_set(info, len, 0);
+ } else {
+ addr = dma_map_single(tx->dev, skb->data, len, DMA_TO_DEVICE);
+ if (unlikely(dma_mapping_error(tx->dev, addr))) {
+ tx->dma_mapping_error++;
+ goto drop;
+ }
+ dma_unmap_len_set(info, len, len);
+ dma_unmap_addr_set(info, dma, addr);
}
- dma_unmap_len_set(info, len, len);
- dma_unmap_addr_set(info, dma, addr);
num_descriptors = 1 + shinfo->nr_frags;
if (hlen < len)
diff --git a/drivers/net/ethernet/google/gve/gve_tx_dqo.c b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
index ad99cbb77e291..ac69793492c9f 100644
--- a/drivers/net/ethernet/google/gve/gve_tx_dqo.c
+++ b/drivers/net/ethernet/google/gve/gve_tx_dqo.c
@@ -176,8 +176,9 @@ static void gve_unmap_packet(struct device *dev,
return;
/* SKB linear portion is guaranteed to be mapped */
- dma_unmap_single(dev, dma_unmap_addr(pkt, dma[0]),
- dma_unmap_len(pkt, len[0]), DMA_TO_DEVICE);
+ if (dma_unmap_len(pkt, len[0]))
+ dma_unmap_single(dev, dma_unmap_addr(pkt, dma[0]),
+ dma_unmap_len(pkt, len[0]), DMA_TO_DEVICE);
for (i = 1; i < pkt->num_bufs; i++) {
netmem_dma_unmap_page_attrs(dev, dma_unmap_addr(pkt, dma[i]),
dma_unmap_len(pkt, len[i]),
@@ -232,6 +233,13 @@ static void gve_tx_free_ring_dqo(struct gve_priv *priv, struct gve_tx_ring *tx,
size_t bytes;
u32 qpl_id;
+ if (tx->tx_hdr_bufs) {
+ dma_free_coherent(hdev,
+ tx->dqo.num_pending_packets * MAX_TCP_HEADER,
+ tx->tx_hdr_bufs, tx->tx_hdr_bufs_dma);
+ tx->tx_hdr_bufs = NULL;
+ }
+
if (tx->q_resources) {
dma_free_coherent(hdev, sizeof(*tx->q_resources),
tx->q_resources, tx->q_resources_bus);
@@ -399,6 +407,12 @@ static int gve_tx_alloc_ring_dqo(struct gve_priv *priv,
if (gve_tx_qpl_buf_init(tx))
goto err;
+ } else if (hdev->dma_pmd_tx_hdrs) {
+ tx->tx_hdr_bufs =
+ dma_alloc_coherent(hdev,
+ tx->dqo.num_pending_packets * MAX_TCP_HEADER,
+ &tx->tx_hdr_bufs_dma,
+ GFP_KERNEL);
}
return 0;
@@ -712,12 +726,20 @@ static int gve_tx_add_skb_no_copy_dqo(struct gve_tx_ring *tx,
u32 len = skb_headlen(skb);
dma_addr_t addr;
- addr = dma_map_single(tx->dev, skb->data, len, DMA_TO_DEVICE);
- if (unlikely(dma_mapping_error(tx->dev, addr)))
- goto err;
+ if (tx->tx_hdr_bufs && len <= MAX_TCP_HEADER) {
+ u32 hdr_off = (u32)completion_tag * MAX_TCP_HEADER;
- dma_unmap_len_set(pkt, len[pkt->num_bufs], len);
- dma_unmap_addr_set(pkt, dma[pkt->num_bufs], addr);
+ memcpy(tx->tx_hdr_bufs + hdr_off, skb->data, len);
+ addr = tx->tx_hdr_bufs_dma + hdr_off;
+ dma_unmap_len_set(pkt, len[pkt->num_bufs], 0);
+ } else {
+ addr = dma_map_single(tx->dev, skb->data, len,
+ DMA_TO_DEVICE);
+ if (unlikely(dma_mapping_error(tx->dev, addr)))
+ goto err;
+ dma_unmap_len_set(pkt, len[pkt->num_bufs], len);
+ dma_unmap_addr_set(pkt, dma[pkt->num_bufs], addr);
+ }
++pkt->num_bufs;
gve_tx_fill_pkt_desc_dqo(tx, desc_idx, enable_csum, len, addr,
@@ -748,10 +770,11 @@ static int gve_tx_add_skb_no_copy_dqo(struct gve_tx_ring *tx,
err:
for (i = 0; i < pkt->num_bufs; i++) {
if (i == 0) {
- dma_unmap_single(tx->dev,
- dma_unmap_addr(pkt, dma[i]),
- dma_unmap_len(pkt, len[i]),
- DMA_TO_DEVICE);
+ if (dma_unmap_len(pkt, len[i]))
+ dma_unmap_single(tx->dev,
+ dma_unmap_addr(pkt, dma[i]),
+ dma_unmap_len(pkt, len[i]),
+ DMA_TO_DEVICE);
} else {
dma_unmap_page(tx->dev,
dma_unmap_addr(pkt, dma[i]),
--
2.56.0.rc1.315.gc6ed9934b7-goog