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[TCP]: simplify microsecond rtt sampling
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Simplify the code that comuputes microsecond rtt estimate used
by TCP Vegas. Move the callback out of the RTT sampler and into
the end of the ack cleanup.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Stephen Hemminger authored and David S. Miller committed Nov 11, 2005
1 parent f4805ed commit 2d2abba
Showing 1 changed file with 30 additions and 32 deletions.
62 changes: 30 additions & 32 deletions net/ipv4/tcp_input.c
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Original file line number Diff line number Diff line change
Expand Up @@ -548,10 +548,9 @@ static void tcp_event_data_recv(struct sock *sk, struct tcp_sock *tp, struct sk_
* To save cycles in the RFC 1323 implementation it was better to break
* it up into three procedures. -- erics
*/
static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt)
{
struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
long m = mrtt; /* RTT */

/* The following amusing code comes from Jacobson's
Expand Down Expand Up @@ -610,9 +609,6 @@ static void tcp_rtt_estimator(struct sock *sk, const __u32 mrtt, u32 *usrtt)
tp->mdev_max = tp->rttvar = max(tp->mdev, TCP_RTO_MIN);
tp->rtt_seq = tp->snd_nxt;
}

if (icsk->icsk_ca_ops->rtt_sample)
icsk->icsk_ca_ops->rtt_sample(sk, *usrtt);
}

/* Calculate rto without backoff. This is the second half of Van Jacobson's
Expand Down Expand Up @@ -1921,7 +1917,7 @@ tcp_fastretrans_alert(struct sock *sk, u32 prior_snd_una,
/* Read draft-ietf-tcplw-high-performance before mucking
* with this code. (Superceeds RFC1323)
*/
static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
static void tcp_ack_saw_tstamp(struct sock *sk, int flag)
{
/* RTTM Rule: A TSecr value received in a segment is used to
* update the averaged RTT measurement only if the segment
Expand All @@ -1940,13 +1936,13 @@ static void tcp_ack_saw_tstamp(struct sock *sk, u32 *usrtt, int flag)
*/
struct tcp_sock *tp = tcp_sk(sk);
const __u32 seq_rtt = tcp_time_stamp - tp->rx_opt.rcv_tsecr;
tcp_rtt_estimator(sk, seq_rtt, usrtt);
tcp_rtt_estimator(sk, seq_rtt);
tcp_set_rto(sk);
inet_csk(sk)->icsk_backoff = 0;
tcp_bound_rto(sk);
}

static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag)
static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, int flag)
{
/* We don't have a timestamp. Can only use
* packets that are not retransmitted to determine
Expand All @@ -1960,21 +1956,21 @@ static void tcp_ack_no_tstamp(struct sock *sk, u32 seq_rtt, u32 *usrtt, int flag
if (flag & FLAG_RETRANS_DATA_ACKED)
return;

tcp_rtt_estimator(sk, seq_rtt, usrtt);
tcp_rtt_estimator(sk, seq_rtt);
tcp_set_rto(sk);
inet_csk(sk)->icsk_backoff = 0;
tcp_bound_rto(sk);
}

static inline void tcp_ack_update_rtt(struct sock *sk, const int flag,
const s32 seq_rtt, u32 *usrtt)
const s32 seq_rtt)
{
const struct tcp_sock *tp = tcp_sk(sk);
/* Note that peer MAY send zero echo. In this case it is ignored. (rfc1323) */
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr)
tcp_ack_saw_tstamp(sk, usrtt, flag);
tcp_ack_saw_tstamp(sk, flag);
else if (seq_rtt >= 0)
tcp_ack_no_tstamp(sk, seq_rtt, usrtt, flag);
tcp_ack_no_tstamp(sk, seq_rtt, flag);
}

static inline void tcp_cong_avoid(struct sock *sk, u32 ack, u32 rtt,
Expand Down Expand Up @@ -2054,20 +2050,27 @@ static int tcp_tso_acked(struct sock *sk, struct sk_buff *skb,
return acked;
}

static inline u32 tcp_usrtt(const struct sk_buff *skb)
{
struct timeval tv, now;

do_gettimeofday(&now);
skb_get_timestamp(skb, &tv);
return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
}

/* Remove acknowledged frames from the retransmission queue. */
static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt)
static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
{
struct tcp_sock *tp = tcp_sk(sk);
const struct inet_connection_sock *icsk = inet_csk(sk);
struct sk_buff *skb;
__u32 now = tcp_time_stamp;
int acked = 0;
__s32 seq_rtt = -1;
struct timeval usnow;
u32 pkts_acked = 0;

if (seq_usrtt)
do_gettimeofday(&usnow);
void (*rtt_sample)(struct sock *sk, u32 usrtt)
= icsk->icsk_ca_ops->rtt_sample;

while ((skb = skb_peek(&sk->sk_write_queue)) &&
skb != sk->sk_send_head) {
Expand Down Expand Up @@ -2107,16 +2110,11 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt
tp->retrans_out -= tcp_skb_pcount(skb);
acked |= FLAG_RETRANS_DATA_ACKED;
seq_rtt = -1;
} else if (seq_rtt < 0)
} else if (seq_rtt < 0) {
seq_rtt = now - scb->when;
if (seq_usrtt) {
struct timeval tv;

skb_get_timestamp(skb, &tv);
*seq_usrtt = (usnow.tv_sec - tv.tv_sec) * 1000000
+ (usnow.tv_usec - tv.tv_usec);
if (rtt_sample)
(*rtt_sample)(sk, tcp_usrtt(skb));
}

if (sacked & TCPCB_SACKED_ACKED)
tp->sacked_out -= tcp_skb_pcount(skb);
if (sacked & TCPCB_LOST)
Expand All @@ -2126,17 +2124,19 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p, s32 *seq_usrtt
!before(scb->end_seq, tp->snd_up))
tp->urg_mode = 0;
}
} else if (seq_rtt < 0)
} else if (seq_rtt < 0) {
seq_rtt = now - scb->when;
if (rtt_sample)
(*rtt_sample)(sk, tcp_usrtt(skb));
}
tcp_dec_pcount_approx(&tp->fackets_out, skb);
tcp_packets_out_dec(tp, skb);
__skb_unlink(skb, &sk->sk_write_queue);
sk_stream_free_skb(sk, skb);
}

if (acked&FLAG_ACKED) {
const struct inet_connection_sock *icsk = inet_csk(sk);
tcp_ack_update_rtt(sk, acked, seq_rtt, seq_usrtt);
tcp_ack_update_rtt(sk, acked, seq_rtt);
tcp_ack_packets_out(sk, tp);

if (icsk->icsk_ca_ops->pkts_acked)
Expand Down Expand Up @@ -2299,7 +2299,6 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
u32 ack = TCP_SKB_CB(skb)->ack_seq;
u32 prior_in_flight;
s32 seq_rtt;
s32 seq_usrtt = 0;
int prior_packets;

/* If the ack is newer than sent or older than previous acks
Expand Down Expand Up @@ -2352,8 +2351,7 @@ static int tcp_ack(struct sock *sk, struct sk_buff *skb, int flag)
prior_in_flight = tcp_packets_in_flight(tp);

/* See if we can take anything off of the retransmit queue. */
flag |= tcp_clean_rtx_queue(sk, &seq_rtt,
icsk->icsk_ca_ops->rtt_sample ? &seq_usrtt : NULL);
flag |= tcp_clean_rtx_queue(sk, &seq_rtt);

if (tp->frto_counter)
tcp_process_frto(sk, prior_snd_una);
Expand Down Expand Up @@ -4242,7 +4240,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
*/
if (tp->rx_opt.saw_tstamp && tp->rx_opt.rcv_tsecr &&
!tp->srtt)
tcp_ack_saw_tstamp(sk, NULL, 0);
tcp_ack_saw_tstamp(sk, 0);

if (tp->rx_opt.tstamp_ok)
tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;
Expand Down

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