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Subject[RFC PATCH v8 15/16] An example how to modifiy NIC driver to use napi_gro_frags() interface
Date
From: Xin Xiaohui <xiaohui.xin@intel.com>

This example is made on ixgbe driver.
It provides API is_rx_buffer_mapped_as_page() to indicate
if the driver use napi_gro_frags() interface or not.
The example allocates 2 pages for DMA for one ring descriptor
using netdev_alloc_page(). When packets is coming, using
napi_gro_frags() to allocate skb and to receive the packets.

---
drivers/net/ixgbe/ixgbe.h | 3 +
drivers/net/ixgbe/ixgbe_main.c | 138 +++++++++++++++++++++++++++++++--------
2 files changed, 112 insertions(+), 29 deletions(-)
diff --git a/drivers/net/ixgbe/ixgbe.h b/drivers/net/ixgbe/ixgbe.h
index 79c35ae..fceffc5 100644
--- a/drivers/net/ixgbe/ixgbe.h
+++ b/drivers/net/ixgbe/ixgbe.h
@@ -131,6 +131,9 @@ struct ixgbe_rx_buffer {
struct page *page;
dma_addr_t page_dma;
unsigned int page_offset;
+ u16 mapped_as_page;
+ struct page *page_skb;
+ unsigned int page_skb_offset;
};

struct ixgbe_queue_stats {
diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
index 6c00ee4..cfe6853 100644
--- a/drivers/net/ixgbe/ixgbe_main.c
+++ b/drivers/net/ixgbe/ixgbe_main.c
@@ -688,6 +688,12 @@ static inline void ixgbe_release_rx_desc(struct ixgbe_hw *hw,
IXGBE_WRITE_REG(hw, IXGBE_RDT(rx_ring->reg_idx), val);
}

+static bool is_rx_buffer_mapped_as_page(struct ixgbe_rx_buffer *bi,
+ struct net_device *dev)
+{
+ return true;
+}
+
/**
* ixgbe_alloc_rx_buffers - Replace used receive buffers; packet split
* @adapter: address of board private structure
@@ -704,13 +710,17 @@ static void ixgbe_alloc_rx_buffers(struct ixgbe_adapter *adapter,
i = rx_ring->next_to_use;
bi = &rx_ring->rx_buffer_info[i];

+
while (cleaned_count--) {
rx_desc = IXGBE_RX_DESC_ADV(*rx_ring, i);

+ bi->mapped_as_page =
+ is_rx_buffer_mapped_as_page(bi, adapter->netdev);
+
if (!bi->page_dma &&
(rx_ring->flags & IXGBE_RING_RX_PS_ENABLED)) {
if (!bi->page) {
- bi->page = alloc_page(GFP_ATOMIC);
+ bi->page = netdev_alloc_page(adapter->netdev);
if (!bi->page) {
adapter->alloc_rx_page_failed++;
goto no_buffers;
@@ -727,7 +737,7 @@ static void ixgbe_alloc_rx_buffers(struct ixgbe_adapter *adapter,
PCI_DMA_FROMDEVICE);
}

- if (!bi->skb) {
+ if (!bi->mapped_as_page && !bi->skb) {
struct sk_buff *skb;
/* netdev_alloc_skb reserves 32 bytes up front!! */
uint bufsz = rx_ring->rx_buf_len + SMP_CACHE_BYTES;
@@ -747,6 +757,19 @@ static void ixgbe_alloc_rx_buffers(struct ixgbe_adapter *adapter,
rx_ring->rx_buf_len,
PCI_DMA_FROMDEVICE);
}
+
+ if (bi->mapped_as_page && !bi->page_skb) {
+ bi->page_skb = netdev_alloc_page(adapter->netdev);
+ if (!bi->page_skb) {
+ adapter->alloc_rx_page_failed++;
+ goto no_buffers;
+ }
+ bi->page_skb_offset = 0;
+ bi->dma = pci_map_page(pdev, bi->page_skb,
+ bi->page_skb_offset,
+ (PAGE_SIZE / 2),
+ PCI_DMA_FROMDEVICE);
+ }
/* Refresh the desc even if buffer_addrs didn't change because
* each write-back erases this info. */
if (rx_ring->flags & IXGBE_RING_RX_PS_ENABLED) {
@@ -823,6 +846,13 @@ struct ixgbe_rsc_cb {
dma_addr_t dma;
};

+static bool is_no_buffer(struct ixgbe_rx_buffer *rx_buffer_info)
+{
+ return ((!rx_buffer_info->skb ||
+ !rx_buffer_info->page_skb) &&
+ !rx_buffer_info->page);
+}
+
#define IXGBE_RSC_CB(skb) ((struct ixgbe_rsc_cb *)(skb)->cb)

static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
@@ -832,6 +862,7 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
struct ixgbe_adapter *adapter = q_vector->adapter;
struct net_device *netdev = adapter->netdev;
struct pci_dev *pdev = adapter->pdev;
+ struct napi_struct *napi = &q_vector->napi;
union ixgbe_adv_rx_desc *rx_desc, *next_rxd;
struct ixgbe_rx_buffer *rx_buffer_info, *next_buffer;
struct sk_buff *skb;
@@ -868,29 +899,57 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
len = le16_to_cpu(rx_desc->wb.upper.length);
}

+ if (is_no_buffer(rx_buffer_info))
+ break;
+
cleaned = true;
- skb = rx_buffer_info->skb;
- prefetch(skb->data);
- rx_buffer_info->skb = NULL;

- if (rx_buffer_info->dma) {
- if ((adapter->flags2 & IXGBE_FLAG2_RSC_ENABLED) &&
- (!(staterr & IXGBE_RXD_STAT_EOP)) &&
- (!(skb->prev)))
- /*
- * When HWRSC is enabled, delay unmapping
- * of the first packet. It carries the
- * header information, HW may still
- * access the header after the writeback.
- * Only unmap it when EOP is reached
- */
- IXGBE_RSC_CB(skb)->dma = rx_buffer_info->dma;
- else
- pci_unmap_single(pdev, rx_buffer_info->dma,
- rx_ring->rx_buf_len,
- PCI_DMA_FROMDEVICE);
- rx_buffer_info->dma = 0;
- skb_put(skb, len);
+ if (!rx_buffer_info->mapped_as_page) {
+ skb = rx_buffer_info->skb;
+ prefetch(skb->data);
+ rx_buffer_info->skb = NULL;
+
+ if (rx_buffer_info->dma) {
+ if ((adapter->flags2 &
+ IXGBE_FLAG2_RSC_ENABLED) &&
+ (!(staterr & IXGBE_RXD_STAT_EOP)) &&
+ (!(skb->prev)))
+ /*
+ * When HWRSC is enabled, delay unmapping
+ * of the first packet. It carries the
+ * header information, HW may still
+ * access the header after the writeback.
+ * Only unmap it when EOP is reached
+ */
+ IXGBE_RSC_CB(skb)->dma =
+ rx_buffer_info->dma;
+ else
+ pci_unmap_single(pdev,
+ rx_buffer_info->dma,
+ rx_ring->rx_buf_len,
+ PCI_DMA_FROMDEVICE);
+ rx_buffer_info->dma = 0;
+ skb_put(skb, len);
+ }
+ } else {
+ skb = napi_get_frags(napi);
+ prefetch(rx_buffer_info->page_skb_offset);
+ rx_buffer_info->skb = NULL;
+ if (rx_buffer_info->dma) {
+ pci_unmap_page(pdev, rx_buffer_info->dma,
+ PAGE_SIZE / 2,
+ PCI_DMA_FROMDEVICE);
+ rx_buffer_info->dma = 0;
+ skb_fill_page_desc(skb,
+ skb_shinfo(skb)->nr_frags,
+ rx_buffer_info->page_skb,
+ rx_buffer_info->page_skb_offset,
+ len);
+ rx_buffer_info->page_skb = NULL;
+ skb->len += len;
+ skb->data_len += len;
+ skb->truesize += len;
+ }
}

if (upper_len) {
@@ -956,6 +1015,12 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
rx_buffer_info->dma = next_buffer->dma;
next_buffer->skb = skb;
next_buffer->dma = 0;
+ if (rx_buffer_info->mapped_as_page) {
+ rx_buffer_info->page_skb =
+ next_buffer->page_skb;
+ next_buffer->page_skb = NULL;
+ next_buffer->skb = NULL;
+ }
} else {
skb->next = next_buffer->skb;
skb->next->prev = skb;
@@ -975,7 +1040,8 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
total_rx_bytes += skb->len;
total_rx_packets++;

- skb->protocol = eth_type_trans(skb, adapter->netdev);
+ if (!rx_buffer_info->mapped_as_page)
+ skb->protocol = eth_type_trans(skb, adapter->netdev);
#ifdef IXGBE_FCOE
/* if ddp, not passing to ULD unless for FCP_RSP or error */
if (adapter->flags & IXGBE_FLAG_FCOE_ENABLED) {
@@ -984,7 +1050,14 @@ static bool ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
goto next_desc;
}
#endif /* IXGBE_FCOE */
- ixgbe_receive_skb(q_vector, skb, staterr, rx_ring, rx_desc);
+
+ if (!rx_buffer_info->mapped_as_page)
+ ixgbe_receive_skb(q_vector, skb, staterr,
+ rx_ring, rx_desc);
+ else {
+ skb_record_rx_queue(skb, rx_ring->queue_index);
+ napi_gro_frags(napi);
+ }

next_desc:
rx_desc->wb.upper.status_error = 0;
@@ -3131,9 +3204,16 @@ static void ixgbe_clean_rx_ring(struct ixgbe_adapter *adapter,

rx_buffer_info = &rx_ring->rx_buffer_info[i];
if (rx_buffer_info->dma) {
- pci_unmap_single(pdev, rx_buffer_info->dma,
- rx_ring->rx_buf_len,
- PCI_DMA_FROMDEVICE);
+ if (!rx_buffer_info->mapped_as_page) {
+ pci_unmap_single(pdev, rx_buffer_info->dma,
+ rx_ring->rx_buf_len,
+ PCI_DMA_FROMDEVICE);
+ } else {
+ pci_unmap_page(pdev, rx_buffer_info->dma,
+ PAGE_SIZE / 2,
+ PCI_DMA_FROMDEVICE);
+ rx_buffer_info->page_skb = NULL;
+ }
rx_buffer_info->dma = 0;
}
if (rx_buffer_info->skb) {
@@ -3158,7 +3238,7 @@ static void ixgbe_clean_rx_ring(struct ixgbe_adapter *adapter,
PAGE_SIZE / 2, PCI_DMA_FROMDEVICE);
rx_buffer_info->page_dma = 0;
}
- put_page(rx_buffer_info->page);
+ netdev_free_page(adapter->netdev, rx_buffer_info->page);
rx_buffer_info->page = NULL;
rx_buffer_info->page_offset = 0;
}
--
1.5.4.4


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