TCP拥塞控制算法 — CUBIC的补丁（3）

TCP拥塞控制算法 — CUBIC的补丁（三）
描述

以下是提交者Stephen Hemminger对这个patch的描述：

fix clock dependency

The hystart code was written with assumption that HZ=1000.

Replace the use of jiffies with bictcp_clock as a millisecond real time clock.

--- a/net/ipv4/tcp_cubic.c+++ b/net/ipv4/tcp_cubic.c@@ -88,7 +88,7 @@ struct bictcp { u32last_time;/* time when updated last_cwnd */ u32bic_origin_point;/* origin point of bic function */ u32bic_K;/* time to origin point from the beginning of the current epoch */-u32delay_min;/* min delay，以前的单位为jiffies*/+u32delay_min;/* min delay (msec << 3)，现在的单位为毫秒*/ u32epoch_start;/* beginning of an epoch */ u32ack_cnt;/* number of acks */ u32tcp_cwnd;/* estimated tcp cwnd */@@ -98,7 +98,7 @@ struct bictcp { u8found;/* the exit point is found? */ u32round_start;/* beginning of each round */ u32end_seq;/* end_seq of the round */-u32last_jiffies;/* last time when the ACK spacing is close，单位为jiffies */+u32last_ack;/* last time when the ACK spacing is close，单位为毫秒 */ u32curr_rtt;/* the minimum rtt of current round */ }; @@ -119,12 +119,21 @@ static inline void bictcp_reset(struct bictcp *ca) ca->found = 0; }             +static inline u32 bictcp_clock(void)+{+#if HZ < 1000 /* NZ小于1000，返回的是实际时间，单位为毫秒 */+return ktime_to_ms(ktime_get_real());+#else+return jiffies_to_msecs(jiffies); /* 返回的是jiffies时间，单位为毫秒*/+#endif+}+ static inline void bictcp_hystart_reset(struct sock *sk) { struct tcp_sock *tp = tcp_sk(sk); struct bictcp *ca = inet_csk_ca(sk); -ca->round_start = ca->last_jiffies = jiffies;+ca->round_start = ca->last_ack = bictcp_clock(); ca->end_seq = tp->snd_nxt; ca->curr_rtt = 0; ca->sample_cnt = 0;@@ -239,8 +248,8 @@ static inline void bictcp_update(struct bictcp *ca, u32 cwnd)  */  /* change the unit from HZ to bictcp_HZ */-t = ((tcp_time_stamp + (ca->delay_min>>3) - ca->epoch_start)-     << BICTCP_HZ) / HZ;+t = ((tcp_time_stamp + msecs_to_jiffies(ca->delay_min>>3)+      - ca->epoch_start) << BICTCP_HZ) / HZ;  if (t < ca->bic_K)/* t - K */ offs = ca->bic_K - t;@@ -342,14 +351,12 @@ static void hystart_update(struct sock *sk, u32 delay) struct bictcp *ca = inet_csk_ca(sk);  if (!(ca->found & hystart_detect)) {-u32 curr_jiffies = jiffies;+u32 now = bictcp_clock();  /* first detection parameter - ack-train detection */-if ((s32)(curr_jiffies - ca->last_jiffies) <=-    msecs_to_jiffies(hystart_ack_delta)) {-ca->last_jiffies = curr_jiffies;-if ((s32) (curr_jiffies - ca->round_start) >-    ca->delay_min >> 4)+if ((s32)(now - ca->last_ack) <= hystart_ack_delta) {+ca->last_ack = now;+if ((s32)(now - ca->round_start) > ca->delay_min >> 4) ca->found |= HYSTART_ACK_TRAIN; } @@ -396,7 +403,7 @@ static void bictcp_acked(struct sock *sk, u32 cnt, s32 rtt_us) if ((s32)(tcp_time_stamp - ca->epoch_start) < HZ) return; -delay = usecs_to_jiffies(rtt_us) << 3;+delay = (rtt_us << 3) / USEC_PER_MSEC; if (delay == 0) delay = 1;

#ifndef _STRUCT_TIMESPEC#define _STRUCT_TIMESPECstruct timespec {    __kernel_time_t tv_sec; /* seconds，long*/    long tv_nsec; /* nanoseconds */};#endifunion ktime {    s64 tv64;#if BITS_PER_LONG != 64 && !defined(CONFIG_KTIME_SCALAR)    struct {#ifdef __BIG_ENDIAN    s32 sec, nsec;#else    s32 nsec, sec;#endif    } tv;#endif};typedef union ktime ktime_t;/** * ktime_get_real - get the real (wall) time in ktime_t format * returns the time in ktime_t format */ktime_t ktime_get_real(void){    struct timespec now;    getnstimeofday(&now);    return timespec_to_ktime(now);}static inline s64 ktime_to_ms(const ktime_t kt){    struct timeval tv = ktime_to_timeval(kt);    return (s64) tv.tv_sec * MSEC_PER_SEC + tv.tv_usec / USEC_PER_MSEC;}/** * ktime_to_timeval - convert a ktime_t variable to timeval format * @kt: the ktime_t variable to convert * Returns the timeval representation of the ktime value */static inline struct timeval ktime_to_timeval (const ktime_t kt){    return (struct timeval) {        .tv_sec = (time_t) kt.tv.sec,        .tv_usec = (suseconds_t) (kt.tv.nsec / NSEC_PER_USEC) };}

原来的bictcp结构中的round_start、delay_min和last_jiffies的单位为jiffies，现在考虑到1jiffies不

一定代表1ms（如果HZ不为1000），所以这三个变量就采用毫秒为单位来计算。原来的版本也没

有错误，现在只是改了下度量单位。

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