net: add gro_cells infrastructure

This adds a new include file (include/net/gro_cells.h), to bring GRO
(Generic Receive Offload) capability to tunnels, in a modular way.

Because tunnels receive path is lockless, and GRO adds a serialization
using a napi_struct, I chose to add an array of up to
DEFAULT_MAX_NUM_RSS_QUEUES cells, so that multi queue devices wont be
slowed down because of GRO layer.

skb_get_rx_queue() is used as selector.

In the future, we might add optional fanout capabilities, using rxhash
for example.

With help from Ben Hutchings who reminded me
netif_get_num_default_rss_queues() function.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 103 insertions, 0 deletions

diff --git a/include/net/gro_cells.h b/include/net/gro_cells.h
new file mode 100644
index 000000000000..4fd8a4b4b7ee
--- /dev/null
+++ b/include/net/gro_cells.h
@@ -0,0 +1,103 @@
+#ifndef _NET_GRO_CELLS_H
+#define _NET_GRO_CELLS_H
+
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/netdevice.h>
+
+struct gro_cell {
+        struct sk_buff_head     napi_skbs;
+        struct napi_struct      napi;
+} ____cacheline_aligned_in_smp;
+
+struct gro_cells {
+        unsigned int            gro_cells_mask;
+        struct gro_cell         *cells;
+};
+
+static inline void gro_cells_receive(struct gro_cells *gcells, struct sk_buff *skb)
+{
+        unsigned long flags;
+        struct gro_cell *cell = gcells->cells;
+        struct net_device *dev = skb->dev;
+
+        if (!cell || skb_cloned(skb) || !(dev->features & NETIF_F_GRO)) {
+                netif_rx(skb);
+                return;
+        }
+
+        if (skb_rx_queue_recorded(skb))
+                cell += skb_get_rx_queue(skb) & gcells->gro_cells_mask;
+
+        if (skb_queue_len(&cell->napi_skbs) > netdev_max_backlog) {
+                atomic_long_inc(&dev->rx_dropped);
+                kfree_skb(skb);
+                return;
+        }
+
+        spin_lock_irqsave(&cell->napi_skbs.lock, flags);
+
+        __skb_queue_tail(&cell->napi_skbs, skb);
+        if (skb_queue_len(&cell->napi_skbs) == 1)
+                napi_schedule(&cell->napi);
+
+        spin_unlock_irqrestore(&cell->napi_skbs.lock, flags);
+}
+
+static inline int gro_cell_poll(struct napi_struct *napi, int budget)
+{
+        struct gro_cell *cell = container_of(napi, struct gro_cell, napi);
+        struct sk_buff *skb;
+        int work_done = 0;
+
+        while (work_done < budget) {
+                skb = skb_dequeue(&cell->napi_skbs);
+                if (!skb)
+                        break;
+
+                napi_gro_receive(napi, skb);
+                work_done++;
+        }
+
+        if (work_done < budget)
+                napi_complete(napi);
+        return work_done;
+}
+
+static inline int gro_cells_init(struct gro_cells *gcells, struct net_device *dev)
+{
+        int i;
+
+        gcells->gro_cells_mask = roundup_pow_of_two(netif_get_num_default_rss_queues()) - 1;
+        gcells->cells = kcalloc(sizeof(struct gro_cell),
+                                gcells->gro_cells_mask + 1,
+                                GFP_KERNEL);
+        if (!gcells->cells)
+                return -ENOMEM;
+
+        for (i = 0; i <= gcells->gro_cells_mask; i++) {
+                struct gro_cell *cell = gcells->cells + i;
+
+                skb_queue_head_init(&cell->napi_skbs);
+                netif_napi_add(dev, &cell->napi, gro_cell_poll, 64);
+                napi_enable(&cell->napi);
+        }
+        return 0;
+}
+
+static inline void gro_cells_destroy(struct gro_cells *gcells)
+{
+        struct gro_cell *cell = gcells->cells;
+        int i;
+
+        if (!cell)
+                return;
+        for (i = 0; i <= gcells->gro_cells_mask; i++,cell++) {
+                netif_napi_del(&cell->napi);
+                skb_queue_purge(&cell->napi_skbs);
+        }
+        kfree(gcells->cells);
+        gcells->cells = NULL;
+}
+
+#endif