tg3: provide frags as skb head

This patch converts tg3 driver, one of our reference drivers, to use new
build_skb() api in frag mode.

Instead of using kmalloc() to allocate the memory block that will be
used by build_skb() as skb->head, we use a page fragment.

This is a followup of patch "net: allow skb->head to be a page fragment"

This allows GRO, TCP coalescing, and splice() to be more efficient.

Incidentally, this also removes SLUB slow path contention in kfree()

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ilpo Järvinen <ilpo.jarvinen@helsinki.fi>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Cc: Matt Carlson <mcarlson@broadcom.com>
Cc: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/drivers/net/ethernet/broadcom/tg3.c b/drivers/net/ethernet/broadcom/tg3.c
index d481b0a..482138e 100644 (file)
--- a/drivers/net/ethernet/broadcom/tg3.c
+++ b/drivers/net/ethernet/broadcom/tg3.c
@@ -195,6 +195,15 @@ static inline void _tg3_flag_clear(enum TG3_FLAGS flag, unsigned long *bits)
 #define TG3_RX_OFFSET(tp)      (NET_SKB_PAD)
 #endif
 
+/* This driver uses the new build_skb() API providing a frag as skb->head
+ * This strategy permits better GRO aggregation, better TCP coalescing, and
+ * better splice() implementation (avoids a copy from head to a page), at
+ * minimal memory cost.
+ * In this 2048 bytes block, we have enough room to store the MTU=1500 frame
+ * and the struct skb_shared_info.
+ */
+#define TG3_FRAGSIZE 2048
+
 /* minimum number of free TX descriptors required to wake up TX process */
 #define TG3_TX_WAKEUP_THRESH(tnapi)            ((tnapi)->tx_pending / 4)
 #define TG3_TX_BD_DMA_MAX_2K           2048
@@ -5617,17 +5626,48 @@ static void tg3_tx(struct tg3_napi *tnapi)
        }
 }
 
+static void *tg3_frag_alloc(struct tg3_rx_prodring_set *tpr)
+{
+       void *data;
+
+       if (tpr->rx_page_size < TG3_FRAGSIZE) {
+               struct page *page = alloc_page(GFP_ATOMIC);
+
+               if (!page)
+                       return NULL;
+               atomic_add((PAGE_SIZE / TG3_FRAGSIZE) - 1, &page->_count);
+               tpr->rx_page_addr = page_address(page);
+               tpr->rx_page_size = PAGE_SIZE;
+       }
+       data = tpr->rx_page_addr;
+       tpr->rx_page_addr += TG3_FRAGSIZE;
+       tpr->rx_page_size -= TG3_FRAGSIZE;
+       return data;
+}
+
+static void tg3_frag_free(bool is_frag, void *data)
+{
+       if (is_frag)
+               put_page(virt_to_head_page(data));
+       else
+               kfree(data);
+}
+
 static void tg3_rx_data_free(struct tg3 *tp, struct ring_info *ri, u32 map_sz)
 {
+       unsigned int skb_size = SKB_DATA_ALIGN(map_sz + TG3_RX_OFFSET(tp)) +
+                  SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
+
        if (!ri->data)
                return;
 
        pci_unmap_single(tp->pdev, dma_unmap_addr(ri, mapping),
                         map_sz, PCI_DMA_FROMDEVICE);
-       kfree(ri->data);
+       tg3_frag_free(skb_size <= TG3_FRAGSIZE, ri->data);
        ri->data = NULL;
 }
 
+
 /* Returns size of skb allocated or < 0 on error.
  *
  * We only need to fill in the address because the other members
@@ -5640,7 +5680,8 @@ static void tg3_rx_data_free(struct tg3 *tp, struct ring_info *ri, u32 map_sz)
  * (to fetch the error flags, vlan tag, checksum, and opaque cookie).
  */
 static int tg3_alloc_rx_data(struct tg3 *tp, struct tg3_rx_prodring_set *tpr,
-                           u32 opaque_key, u32 dest_idx_unmasked)
+                            u32 opaque_key, u32 dest_idx_unmasked,
+                            unsigned int *frag_size)
 {
        struct tg3_rx_buffer_desc *desc;
        struct ring_info *map;
@@ -5675,7 +5716,13 @@ static int tg3_alloc_rx_data(struct tg3 *tp, struct tg3_rx_prodring_set *tpr,
         */
        skb_size = SKB_DATA_ALIGN(data_size + TG3_RX_OFFSET(tp)) +
                   SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
-       data = kmalloc(skb_size, GFP_ATOMIC);
+       if (skb_size <= TG3_FRAGSIZE) {
+               data = tg3_frag_alloc(tpr);
+               *frag_size = TG3_FRAGSIZE;
+       } else {
+               data = kmalloc(skb_size, GFP_ATOMIC);
+               *frag_size = 0;
+       }
        if (!data)
                return -ENOMEM;
 
@@ -5683,8 +5730,8 @@ static int tg3_alloc_rx_data(struct tg3 *tp, struct tg3_rx_prodring_set *tpr,
                                 data + TG3_RX_OFFSET(tp),
                                 data_size,
                                 PCI_DMA_FROMDEVICE);
-       if (pci_dma_mapping_error(tp->pdev, mapping)) {
-               kfree(data);
+       if (unlikely(pci_dma_mapping_error(tp->pdev, mapping))) {
+               tg3_frag_free(skb_size <= TG3_FRAGSIZE, data);
                return -EIO;
        }
 
@@ -5835,18 +5882,19 @@ static int tg3_rx(struct tg3_napi *tnapi, int budget)
 
                if (len > TG3_RX_COPY_THRESH(tp)) {
                        int skb_size;
+                       unsigned int frag_size;
 
                        skb_size = tg3_alloc_rx_data(tp, tpr, opaque_key,
-                                                   *post_ptr);
+                                                   *post_ptr, &frag_size);
                        if (skb_size < 0)
                                goto drop_it;
 
                        pci_unmap_single(tp->pdev, dma_addr, skb_size,
                                         PCI_DMA_FROMDEVICE);
 
-                       skb = build_skb(data, 0);
+                       skb = build_skb(data, frag_size);
                        if (!skb) {
-                               kfree(data);
+                               tg3_frag_free(frag_size != 0, data);
                                goto drop_it_no_recycle;
                        }
                        skb_reserve(skb, TG3_RX_OFFSET(tp));
@@ -7279,7 +7327,10 @@ static int tg3_rx_prodring_alloc(struct tg3 *tp,
 
        /* Now allocate fresh SKBs for each rx ring. */
        for (i = 0; i < tp->rx_pending; i++) {
-               if (tg3_alloc_rx_data(tp, tpr, RXD_OPAQUE_RING_STD, i) < 0) {
+               unsigned int frag_size;
+
+               if (tg3_alloc_rx_data(tp, tpr, RXD_OPAQUE_RING_STD, i,
+                                     &frag_size) < 0) {
                        netdev_warn(tp->dev,
                                    "Using a smaller RX standard ring. Only "
                                    "%d out of %d buffers were allocated "
@@ -7311,7 +7362,10 @@ static int tg3_rx_prodring_alloc(struct tg3 *tp,
        }
 
        for (i = 0; i < tp->rx_jumbo_pending; i++) {
-               if (tg3_alloc_rx_data(tp, tpr, RXD_OPAQUE_RING_JUMBO, i) < 0) {
+               unsigned int frag_size;
+
+               if (tg3_alloc_rx_data(tp, tpr, RXD_OPAQUE_RING_JUMBO, i,
+                                     &frag_size) < 0) {
                        netdev_warn(tp->dev,
                                    "Using a smaller RX jumbo ring. Only %d "
                                    "out of %d buffers were allocated "

diff --git a/drivers/net/ethernet/broadcom/tg3.h b/drivers/net/ethernet/broadcom/tg3.h
index 93865f8..7c85545 100644 (file)
--- a/drivers/net/ethernet/broadcom/tg3.h
+++ b/drivers/net/ethernet/broadcom/tg3.h
@@ -2815,6 +2815,8 @@ struct tg3_rx_prodring_set {
        struct ring_info                *rx_jmb_buffers;
        dma_addr_t                      rx_std_mapping;
        dma_addr_t                      rx_jmb_mapping;
+       void                            *rx_page_addr;
+       unsigned int                    rx_page_size;
 };
 
 #define TG3_IRQ_MAX_VECS_RSS           5