tcp: do not scale TSO segment size with reordering degree

Since 2005 (c1b4a7e69576d65efc31a8cea0714173c2841244)
tcp_tso_should_defer has been using tcp_max_burst() as a target limit
for deciding how large to make outgoing TSO packets when not using
sysctl_tcp_tso_win_divisor. But since 2008
(dd9e0dda66ba38a2ddd1405ac279894260dc5c36) tcp_max_burst() returns the
reordering degree. We should not have tcp_tso_should_defer attempt to
build larger segments just because there is more reordering. This
commit splits the notion of deferral size used in TSO from the notion
of burst size used in cwnd moderation, and returns the TSO deferral
limit to its original value.

Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/include/net/tcp.h b/include/net/tcp.h
index 113160b845888a6e849c8b34e7d5a1311728090d..87e3c80bfa00216f18841cb29ce72cbdf3b8151a 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -834,6 +834,14 @@ static inline __u32 tcp_current_ssthresh(const struct sock *sk)
 extern void tcp_enter_cwr(struct sock *sk, const int set_ssthresh);
 extern __u32 tcp_init_cwnd(const struct tcp_sock *tp, const struct dst_entry *dst);
 
+/* The maximum number of MSS of available cwnd for which TSO defers
+ * sending if not using sysctl_tcp_tso_win_divisor.
+ */
+static inline __u32 tcp_max_tso_deferred_mss(const struct tcp_sock *tp)
+{
+       return 3;
+}
+
 /* Slow start with delack produces 3 packets of burst, so that
  * it is safe "de facto".  This will be the default - same as
  * the default reordering threshold - but if reordering increases,

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 850c737e08e2a4a9185c64c8776711d83b8c7b08..fc6d475f488f87a9bb084e9b9930e8e28cf7757f 100644 (file)
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -292,7 +292,7 @@ int tcp_is_cwnd_limited(const struct sock *sk, u32 in_flight)
            left * sysctl_tcp_tso_win_divisor < tp->snd_cwnd &&
            left * tp->mss_cache < sk->sk_gso_max_size)
                return 1;
-       return left <= tcp_max_burst(tp);
+       return left <= tcp_max_tso_deferred_mss(tp);
 }
 EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
 

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 63170e29754003c78b2cce548425ae1710c317c4..58f69acd3d2254b6ce48e1847665c3c49cb7a1d9 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1581,7 +1581,7 @@ static int tcp_tso_should_defer(struct sock *sk, struct sk_buff *skb)
                 * frame, so if we have space for more than 3 frames
                 * then send now.
                 */
-               if (limit > tcp_max_burst(tp) * tp->mss_cache)
+               if (limit > tcp_max_tso_deferred_mss(tp) * tp->mss_cache)
                        goto send_now;
        }