Merge branch 'tcp-remove-non-GSO-code'

Eric Dumazet says:

====================
tcp: remove non GSO code

Switching TCP to GSO mode, relying on core networking layers
to perform eventual adaptation for dumb devices was overdue.

1) Most TCP developments are done with TSO in mind.
2) Less high-resolution timers needs to be armed for TCP-pacing
3) GSO can benefit of xmit_more hint
4) Receiver GRO is more effective (as if TSO was used for real on sender)
   -> less ACK packets and overhead.
5) Write queues have less overhead (one skb holds about 64KB of payload)
6) SACK coalescing just works. (no payload in skb->head)
7) rtx rb-tree contains less packets, SACK is cheaper.
8) Removal of legacy code. Less maintenance hassles.

Note that I have left the sendpage/zerocopy paths, but they probably can
benefit from the same strategy.

Thanks to Oleksandr Natalenko for reporting a performance issue for BBR/fq_codel,
which was the main reason I worked on this patch series.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 34 deletions

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b2bca373f8bee..8795d76f987c6 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1206,7 +1206,7 @@ static void tcp_queue_skb(struct sock *sk, struct sk_buff *skb)
 /* Initialize TSO segments for a packet. */
 static void tcp_set_skb_tso_segs(struct sk_buff *skb, unsigned int mss_now)
 {
-	if (skb->len <= mss_now || skb->ip_summed == CHECKSUM_NONE) {
+	if (skb->len <= mss_now) {
 		/* Avoid the costly divide in the normal
 		 * non-TSO case.
 		 */
@@ -1335,21 +1335,9 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 	TCP_SKB_CB(buff)->sacked = TCP_SKB_CB(skb)->sacked;
 	tcp_skb_fragment_eor(skb, buff);
 
-	if (!skb_shinfo(skb)->nr_frags && skb->ip_summed != CHECKSUM_PARTIAL) {
-		/* Copy and checksum data tail into the new buffer. */
-		buff->csum = csum_partial_copy_nocheck(skb->data + len,
-						       skb_put(buff, nsize),
-						       nsize, 0);
-
-		skb_trim(skb, len);
-
-		skb->csum = csum_block_sub(skb->csum, buff->csum, len);
-	} else {
-		skb->ip_summed = CHECKSUM_PARTIAL;
-		skb_split(skb, buff, len);
-	}
+	skb_split(skb, buff, len);
 
-	buff->ip_summed = skb->ip_summed;
+	buff->ip_summed = CHECKSUM_PARTIAL;
 
 	buff->tstamp = skb->tstamp;
 	tcp_fragment_tstamp(skb, buff);
@@ -1901,7 +1889,7 @@ static int tso_fragment(struct sock *sk, enum tcp_queue tcp_queue,
 
 	tcp_skb_fragment_eor(skb, buff);
 
-	buff->ip_summed = skb->ip_summed = CHECKSUM_PARTIAL;
+	buff->ip_summed = CHECKSUM_PARTIAL;
 	skb_split(skb, buff, len);
 	tcp_fragment_tstamp(skb, buff);
 
@@ -2134,7 +2122,7 @@ static int tcp_mtu_probe(struct sock *sk)
 	TCP_SKB_CB(nskb)->tcp_flags = TCPHDR_ACK;
 	TCP_SKB_CB(nskb)->sacked = 0;
 	nskb->csum = 0;
-	nskb->ip_summed = skb->ip_summed;
+	nskb->ip_summed = CHECKSUM_PARTIAL;
 
 	tcp_insert_write_queue_before(nskb, skb, sk);
 	tcp_highest_sack_replace(sk, skb, nskb);
@@ -2142,14 +2130,7 @@ static int tcp_mtu_probe(struct sock *sk)
 	len = 0;
 	tcp_for_write_queue_from_safe(skb, next, sk) {
 		copy = min_t(int, skb->len, probe_size - len);
-		if (nskb->ip_summed) {
-			skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
-		} else {
-			__wsum csum = skb_copy_and_csum_bits(skb, 0,
-							     skb_put(nskb, copy),
-							     copy, 0);
-			nskb->csum = csum_block_add(nskb->csum, csum, len);
-		}
+		skb_copy_bits(skb, 0, skb_put(nskb, copy), copy);
 
 		if (skb->len <= copy) {
 			/* We've eaten all the data from this skb.
@@ -2166,9 +2147,6 @@ static int tcp_mtu_probe(struct sock *sk)
 						   ~(TCPHDR_FIN|TCPHDR_PSH);
 			if (!skb_shinfo(skb)->nr_frags) {
 				skb_pull(skb, copy);
-				if (skb->ip_summed != CHECKSUM_PARTIAL)
-					skb->csum = csum_partial(skb->data,
-								 skb->len, 0);
 			} else {
 				__pskb_trim_head(skb, copy);
 				tcp_set_skb_tso_segs(skb, mss_now);
@@ -2746,12 +2724,6 @@ static bool tcp_collapse_retrans(struct sock *sk, struct sk_buff *skb)
 	}
 	tcp_highest_sack_replace(sk, next_skb, skb);
 
-	if (next_skb->ip_summed == CHECKSUM_PARTIAL)
-		skb->ip_summed = CHECKSUM_PARTIAL;
-
-	if (skb->ip_summed != CHECKSUM_PARTIAL)
-		skb->csum = csum_block_add(skb->csum, next_skb->csum, skb_size);
-
 	/* Update sequence range on original skb. */
 	TCP_SKB_CB(skb)->end_seq = TCP_SKB_CB(next_skb)->end_seq;