sfc: Feed GRO result into RX allocation policy and interrupt moderation

When GRO is successfully merging received packets, we should allocate
raw page buffers rather than skbs that will be discarded by GRO.
Otherwise, we should allocate skbs.

GRO also benefits from higher interrupt moderation, so increase the
score for mergeable RX packets.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/sfc/rx.c

@@ -445,6 +445,7 @@ static void efx_rx_packet_lro(struct efx_channel *channel,
 			      bool checksummed)
 {
 	struct napi_struct *napi = &channel->napi_str;
+	gro_result_t gro_result;
 
 	/* Pass the skb/page into the LRO engine */
 	if (rx_buf->page) {
@@ -452,6 +453,7 @@ static void efx_rx_packet_lro(struct efx_channel *channel,
 
 		if (!skb) {
 			put_page(rx_buf->page);
+			gro_result = GRO_DROP;
 			goto out;
 		}
 
@@ -467,7 +469,7 @@ static void efx_rx_packet_lro(struct efx_channel *channel,
 		skb->ip_summed =
 			checksummed ? CHECKSUM_UNNECESSARY : CHECKSUM_NONE;
 
-		napi_gro_frags(napi);
+		gro_result = napi_gro_frags(napi);
 
 out:
 		EFX_BUG_ON_PARANOID(rx_buf->skb);
@@ -476,9 +478,16 @@ static void efx_rx_packet_lro(struct efx_channel *channel,
 		EFX_BUG_ON_PARANOID(!rx_buf->skb);
 		EFX_BUG_ON_PARANOID(!checksummed);
 
-		napi_gro_receive(napi, rx_buf->skb);
+		gro_result = napi_gro_receive(napi, rx_buf->skb);
 		rx_buf->skb = NULL;
 	}
+
+	if (gro_result == GRO_NORMAL) {
+		channel->rx_alloc_level += RX_ALLOC_FACTOR_SKB;
+	} else if (gro_result != GRO_DROP) {
+		channel->rx_alloc_level += RX_ALLOC_FACTOR_LRO;
+		channel->irq_mod_score += 2;
+	}
 }
 
 void efx_rx_packet(struct efx_rx_queue *rx_queue, unsigned int index,