tcp: TSO packets automatic sizing

[karo-tx-linux.git] / net / ipv4 / tcp_input.c

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index ec492eae0cd75684cc83d0bce697eb39fb37fdd5..1a84fffe6993de90202021b708747ba9cf5b8782 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -688,6 +688,34 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
        }
 }
 
+/* Set the sk_pacing_rate to allow proper sizing of TSO packets.
+ * Note: TCP stack does not yet implement pacing.
+ * FQ packet scheduler can be used to implement cheap but effective
+ * TCP pacing, to smooth the burst on large writes when packets
+ * in flight is significantly lower than cwnd (or rwin)
+ */
+static void tcp_update_pacing_rate(struct sock *sk)
+{
+       const struct tcp_sock *tp = tcp_sk(sk);
+       u64 rate;
+
+       /* set sk_pacing_rate to 200 % of current rate (mss * cwnd / srtt) */
+       rate = (u64)tp->mss_cache * 2 * (HZ << 3);
+
+       rate *= max(tp->snd_cwnd, tp->packets_out);
+
+       /* Correction for small srtt : minimum srtt being 8 (1 jiffy << 3),
+        * be conservative and assume srtt = 1 (125 us instead of 1.25 ms)
+        * We probably need usec resolution in the future.
+        * Note: This also takes care of possible srtt=0 case,
+        * when tcp_rtt_estimator() was not yet called.
+        */
+       if (tp->srtt > 8 + 2)
+               do_div(rate, tp->srtt);
+
+       sk->sk_pacing_rate = min_t(u64, rate, ~0U);
+}
+
 /* Calculate rto without backoff.  This is the second half of Van Jacobson's
  * routine referred to above.
  */
@@ -3278,7 +3306,7 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
        u32 ack_seq = TCP_SKB_CB(skb)->seq;
        u32 ack = TCP_SKB_CB(skb)->ack_seq;
        bool is_dupack = false;
-       u32 prior_in_flight;
+       u32 prior_in_flight, prior_cwnd = tp->snd_cwnd, prior_rtt = tp->srtt;
        u32 prior_fackets;
        int prior_packets = tp->packets_out;
        const int prior_unsacked = tp->packets_out - tp->sacked_out;
@@ -3383,6 +3411,8 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
 
        if (icsk->icsk_pending == ICSK_TIME_RETRANS)
                tcp_schedule_loss_probe(sk);
+       if (tp->srtt != prior_rtt || tp->snd_cwnd != prior_cwnd)
+               tcp_update_pacing_rate(sk);
        return 1;
 
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