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authorEric Dumazet <edumazet@google.com>2017-05-17 00:00:14 +0300
committerDavid S. Miller <davem@davemloft.net>2017-05-17 23:06:01 +0300
commit9a568de4818dea9a05af141046bd3e589245ab83 (patch)
tree6f1502edf55ecb7205660d62bd683ebcf912cfea /net/ipv4/tcp_bbr.c
parentac9517fcf310327fa3e3b0d8366e4b11236b1b4b (diff)
downloadlinux-9a568de4818dea9a05af141046bd3e589245ab83.tar.xz
tcp: switch TCP TS option (RFC 7323) to 1ms clock
TCP Timestamps option is defined in RFC 7323 Traditionally on linux, it has been tied to the internal 'jiffies' variable, because it had been a cheap and good enough generator. For TCP flows on the Internet, 1 ms resolution would be much better than 4ms or 10ms (HZ=250 or HZ=100 respectively) For TCP flows in the DC, Google has used usec resolution for more than two years with great success [1] Receive size autotuning (DRS) is indeed more precise and converges faster to optimal window size. This patch converts tp->tcp_mstamp to a plain u64 value storing a 1 usec TCP clock. This choice will allow us to upstream the 1 usec TS option as discussed in IETF 97. [1] https://www.ietf.org/proceedings/97/slides/slides-97-tcpm-tcp-options-for-low-latency-00.pdf Signed-off-by: Eric Dumazet <edumazet@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/ipv4/tcp_bbr.c')
-rw-r--r--net/ipv4/tcp_bbr.c22
1 files changed, 11 insertions, 11 deletions
diff --git a/net/ipv4/tcp_bbr.c b/net/ipv4/tcp_bbr.c
index 40dc4fc5f6ac..dbcc9352a48f 100644
--- a/net/ipv4/tcp_bbr.c
+++ b/net/ipv4/tcp_bbr.c
@@ -91,7 +91,7 @@ struct bbr {
struct minmax bw; /* Max recent delivery rate in pkts/uS << 24 */
u32 rtt_cnt; /* count of packet-timed rounds elapsed */
u32 next_rtt_delivered; /* scb->tx.delivered at end of round */
- struct skb_mstamp cycle_mstamp; /* time of this cycle phase start */
+ u64 cycle_mstamp; /* time of this cycle phase start */
u32 mode:3, /* current bbr_mode in state machine */
prev_ca_state:3, /* CA state on previous ACK */
packet_conservation:1, /* use packet conservation? */
@@ -411,7 +411,7 @@ static bool bbr_is_next_cycle_phase(struct sock *sk,
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
bool is_full_length =
- skb_mstamp_us_delta(&tp->delivered_mstamp, &bbr->cycle_mstamp) >
+ tcp_stamp_us_delta(tp->delivered_mstamp, bbr->cycle_mstamp) >
bbr->min_rtt_us;
u32 inflight, bw;
@@ -497,7 +497,7 @@ static void bbr_reset_lt_bw_sampling_interval(struct sock *sk)
struct tcp_sock *tp = tcp_sk(sk);
struct bbr *bbr = inet_csk_ca(sk);
- bbr->lt_last_stamp = tp->delivered_mstamp.stamp_jiffies;
+ bbr->lt_last_stamp = div_u64(tp->delivered_mstamp, USEC_PER_MSEC);
bbr->lt_last_delivered = tp->delivered;
bbr->lt_last_lost = tp->lost;
bbr->lt_rtt_cnt = 0;
@@ -551,7 +551,7 @@ static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs)
struct bbr *bbr = inet_csk_ca(sk);
u32 lost, delivered;
u64 bw;
- s32 t;
+ u32 t;
if (bbr->lt_use_bw) { /* already using long-term rate, lt_bw? */
if (bbr->mode == BBR_PROBE_BW && bbr->round_start &&
@@ -603,15 +603,15 @@ static void bbr_lt_bw_sampling(struct sock *sk, const struct rate_sample *rs)
return;
/* Find average delivery rate in this sampling interval. */
- t = (s32)(tp->delivered_mstamp.stamp_jiffies - bbr->lt_last_stamp);
- if (t < 1)
- return; /* interval is less than one jiffy, so wait */
- t = jiffies_to_usecs(t);
- /* Interval long enough for jiffies_to_usecs() to return a bogus 0? */
- if (t < 1) {
+ t = div_u64(tp->delivered_mstamp, USEC_PER_MSEC) - bbr->lt_last_stamp;
+ if ((s32)t < 1)
+ return; /* interval is less than one ms, so wait */
+ /* Check if can multiply without overflow */
+ if (t >= ~0U / USEC_PER_MSEC) {
bbr_reset_lt_bw_sampling(sk); /* interval too long; reset */
return;
}
+ t *= USEC_PER_MSEC;
bw = (u64)delivered * BW_UNIT;
do_div(bw, t);
bbr_lt_bw_interval_done(sk, bw);
@@ -825,7 +825,7 @@ static void bbr_init(struct sock *sk)
bbr->idle_restart = 0;
bbr->full_bw = 0;
bbr->full_bw_cnt = 0;
- bbr->cycle_mstamp.v64 = 0;
+ bbr->cycle_mstamp = 0;
bbr->cycle_idx = 0;
bbr_reset_lt_bw_sampling(sk);
bbr_reset_startup_mode(sk);