[RFC PATCH v2 3/5] tcp: added get_segs_per_round

[Natale Patriciello]

Usually, the pacing time is provided per-segment. In some occasion, this
time refers to the time between a group of segments. With this commit, add
the possibility for the congestion control module to tell the TCP socket
how many segments can be sent out before pausing and setting a pacing
timer.

Signed-off-by: Natale Patriciello <natale.patricie...@gmail.com>
---
 include/net/tcp.h     |  2 ++
 net/ipv4/tcp_output.c | 13 +++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/include/net/tcp.h b/include/net/tcp.h
index e817f0669d0e..3561eca5a61f 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1019,6 +1019,8 @@ struct tcp_congestion_ops {
        u64 (*get_pacing_time)(struct sock *sk);
        /* the pacing timer is expired (optional) */
        void (*pacing_timer_expired)(struct sock *sk);
+       /* get the # segs to send out when the timer expires (optional) */
+       u32 (*get_segs_per_round)(struct sock *sk);
 
        char            name[TCP_CA_NAME_MAX];
        struct module   *owner;
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 25b4cf0802f2..e37941e4328b 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2249,6 +2249,7 @@ static bool tcp_write_xmit(struct sock *sk, unsigned int 
mss_now, int nonagle,
        int result;
        bool is_cwnd_limited = false, is_rwnd_limited = false;
        u32 max_segs;
+       u32 pacing_allowed_segs = 0;
 
        sent_pkts = 0;
 
@@ -2265,14 +2266,18 @@ static bool tcp_write_xmit(struct sock *sk, unsigned 
int mss_now, int nonagle,
        max_segs = tcp_tso_segs(sk, mss_now);
        tcp_mstamp_refresh(tp);
 
-       if (!tcp_pacing_timer_check(sk) &&
-           ca_ops && ca_ops->pacing_timer_expired)
-               ca_ops->pacing_timer_expired(sk);
+       if (!tcp_pacing_timer_check(sk)) {
+               pacing_allowed_segs = 1;
+               if (ca_ops && ca_ops->pacing_timer_expired)
+                       ca_ops->pacing_timer_expired(sk);
+               if (ca_ops && ca_ops->get_segs_per_round)
+                       pacing_allowed_segs = ca_ops->get_segs_per_round(sk);
+       }
 
        while ((skb = tcp_send_head(sk))) {
                unsigned int limit;
 
-               if (tcp_pacing_check(sk))
+               if (sent_pkts >= pacing_allowed_segs)
                        break;
 
                tso_segs = tcp_init_tso_segs(skb, mss_now);
-- 
2.14.2