netdev - [RFC PATCH v2 net-next 1/3] sfc: don't score irq moderation points for GRO

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Message-ID: <eb027202-2a70-12eb-1544-7ddfd137aabb@solarflare.com>
Date:   Tue, 30 Jul 2019 23:20:58 +0100
From:   Edward Cree <ecree@...arflare.com>
To:     <linux-net-drivers@...arflare.com>,
        David Miller <davem@...emloft.net>
CC:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>
Subject: [RFC PATCH v2 net-next 1/3] sfc: don't score irq moderation points
 for GRO

We already scored points when handling the RX event, no-one else does this,
 and looking at the history it appears this was originally meant to only
 score on merges, not on GRO_NORMAL.  Moreover, it gets in the way of
 changing GRO to not immediately pass GRO_NORMAL skbs to the stack.
Performance testing with four TCP streams received on a single CPU (where
 throughput was line rate of 9.4Gbps in all tests) showed a 13.7% reduction
 in RX CPU usage (n=6, p=0.03).

Signed-off-by: Edward Cree <ecree@...arflare.com>
---
 drivers/net/ethernet/sfc/rx.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/sfc/rx.c b/drivers/net/ethernet/sfc/rx.c
index d5db045535d3..85ec07f5a674 100644
--- a/drivers/net/ethernet/sfc/rx.c
+++ b/drivers/net/ethernet/sfc/rx.c
@@ -412,7 +412,6 @@ efx_rx_packet_gro(struct efx_channel *channel, struct efx_rx_buffer *rx_buf,
 		  unsigned int n_frags, u8 *eh)
 {
 	struct napi_struct *napi = &channel->napi_str;
-	gro_result_t gro_result;
 	struct efx_nic *efx = channel->efx;
 	struct sk_buff *skb;
 
@@ -449,9 +448,7 @@ efx_rx_packet_gro(struct efx_channel *channel, struct efx_rx_buffer *rx_buf,
 
 	skb_record_rx_queue(skb, channel->rx_queue.core_index);
 
-	gro_result = napi_gro_frags(napi);
-	if (gro_result != GRO_DROP)
-		channel->irq_mod_score += 2;
+	napi_gro_frags(napi);
 }
 
 /* Allocate and construct an SKB around page fragments */