tcp_bbr: better deal with suboptimal GSO (II)

This is second part of dealing with suboptimal device gso parameters.
In first patch (350c9f484bde "tcp_bbr: better deal with suboptimal GSO")
we dealt with devices having low gso_max_segs

Some devices lower gso_max_size from 64KB to 16 KB (r8152 is an example)

In order to probe an optimal cwnd, we want BBR being not sensitive
to whatever GSO constraint a device can have.

This patch removes tso_segs_goal() CC callback in favor of
min_tso_segs() for CC wanting to override sysctl_tcp_min_tso_segs

Next patch will remove bbr->tso_segs_goal since it does not have
to be persistent.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-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 92b06c6..9c9b376 100644 (file)
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -511,8 +511,6 @@ __u32 cookie_v6_init_sequence(const struct sk_buff *skb, __u16 *mss);
 #endif
 /* tcp_output.c */
 
-u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
-                    int min_tso_segs);
 void __tcp_push_pending_frames(struct sock *sk, unsigned int cur_mss,
                               int nonagle);
 int __tcp_retransmit_skb(struct sock *sk, struct sk_buff *skb, int segs);
@@ -981,8 +979,8 @@ struct tcp_congestion_ops {
        u32  (*undo_cwnd)(struct sock *sk);
        /* hook for packet ack accounting (optional) */
        void (*pkts_acked)(struct sock *sk, const struct ack_sample *sample);
-       /* suggest number of segments for each skb to transmit (optional) */
-       u32 (*tso_segs_goal)(struct sock *sk);
+       /* override sysctl_tcp_min_tso_segs */
+       u32 (*min_tso_segs)(struct sock *sk);
        /* returns the multiplier used in tcp_sndbuf_expand (optional) */
        u32 (*sndbuf_expand)(struct sock *sk);
        /* call when packets are delivered to update cwnd and pacing rate,

diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index a471f69..afc0567 100644 (file)
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -261,23 +261,26 @@ static void bbr_set_pacing_rate(struct sock *sk, u32 bw, int gain)
                sk->sk_pacing_rate = rate;
 }
 
-/* Return count of segments we want in the skbs we send, or 0 for default. */
-static u32 bbr_tso_segs_goal(struct sock *sk)
+/* override sysctl_tcp_min_tso_segs */
+static u32 bbr_min_tso_segs(struct sock *sk)
 {
-       struct bbr *bbr = inet_csk_ca(sk);
-
-       return bbr->tso_segs_goal;
+       return sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
 }
 
 static void bbr_set_tso_segs_goal(struct sock *sk)
 {
        struct tcp_sock *tp = tcp_sk(sk);
        struct bbr *bbr = inet_csk_ca(sk);
-       u32 min_segs;
+       u32 segs, bytes;
+
+       /* Sort of tcp_tso_autosize() but ignoring
+        * driver provided sk_gso_max_size.
+        */
+       bytes = min_t(u32, sk->sk_pacing_rate >> sk->sk_pacing_shift,
+                     GSO_MAX_SIZE - 1 - MAX_TCP_HEADER);
+       segs = max_t(u32, bytes / tp->mss_cache, bbr_min_tso_segs(sk));
 
-       min_segs = sk->sk_pacing_rate < (bbr_min_tso_rate >> 3) ? 1 : 2;
-       bbr->tso_segs_goal = min(tcp_tso_autosize(sk, tp->mss_cache, min_segs),
-                                0x7FU);
+       bbr->tso_segs_goal = min(segs, 0x7FU);
 }
 
 /* Save "last known good" cwnd so we can restore it after losses or PROBE_RTT */
@@ -936,7 +939,7 @@ static struct tcp_congestion_ops tcp_bbr_cong_ops __read_mostly = {
        .undo_cwnd      = bbr_undo_cwnd,
        .cwnd_event     = bbr_cwnd_event,
        .ssthresh       = bbr_ssthresh,
-       .tso_segs_goal  = bbr_tso_segs_goal,
+       .min_tso_segs   = bbr_min_tso_segs,
        .get_info       = bbr_get_info,
        .set_state      = bbr_set_state,
 };

diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 49d043d..383cac0 100644 (file)
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1703,8 +1703,8 @@ static bool tcp_nagle_check(bool partial, const struct tcp_sock *tp,
 /* Return how many segs we'd like on a TSO packet,
  * to send one TSO packet per ms
  */
-u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
-                    int min_tso_segs)
+static u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
+                           int min_tso_segs)
 {
        u32 bytes, segs;
 
@@ -1720,7 +1720,6 @@ u32 tcp_tso_autosize(const struct sock *sk, unsigned int mss_now,
 
        return segs;
 }
-EXPORT_SYMBOL(tcp_tso_autosize);
 
 /* Return the number of segments we want in the skb we are transmitting.
  * See if congestion control module wants to decide; otherwise, autosize.
@@ -1728,11 +1727,13 @@ EXPORT_SYMBOL(tcp_tso_autosize);
 static u32 tcp_tso_segs(struct sock *sk, unsigned int mss_now)
 {
        const struct tcp_congestion_ops *ca_ops = inet_csk(sk)->icsk_ca_ops;
-       u32 tso_segs = ca_ops->tso_segs_goal ? ca_ops->tso_segs_goal(sk) : 0;
+       u32 min_tso, tso_segs;
 
-       if (!tso_segs)
-               tso_segs = tcp_tso_autosize(sk, mss_now,
-                               sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs);
+       min_tso = ca_ops->min_tso_segs ?
+                       ca_ops->min_tso_segs(sk) :
+                       sock_net(sk)->ipv4.sysctl_tcp_min_tso_segs;
+
+       tso_segs = tcp_tso_autosize(sk, mss_now, min_tso);
        return min_t(u32, tso_segs, sk->sk_gso_max_segs);
 }