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tcp_bbr: better deal with suboptimal GSO (II) 

This is second part of dealing with suboptimal device gso parameters.
In first patch (350c9f484b "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>
This commit is contained in:
Eric Dumazet 2018-02-28 14:40:46 -08:00 committed by David S. Miller
parent 7797dc4141
commit dcb8c9b437
3 changed files with 23 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/net/tcp.h
View File

@ -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,

23
net/ipv4/tcp_bbr.c
View File

@ -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;
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);
/* 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));
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,
};

15
net/ipv4/tcp_output.c
View File

@ -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);
}