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Message-ID: <D1D6D627.5ED3%brakmo@fb.com>
Date: Fri, 24 Jul 2015 00:47:36 +0000
From: Lawrence Brakmo <brakmo@...com>
To: Yuchung Cheng <ycheng@...gle.com>
CC: netdev <netdev@...r.kernel.org>, Kernel Team <Kernel-team@...com>,
"Neal Cardwell" <ncardwell@...gle.com>,
Eric Dumazet <eric.dumazet@...il.com>
Subject: Re: [RFC PATCH v2 net-next 3/3] tcp: add NV congestion control
Thank you all for your comments, I¹m currently testing the changes.
Other comments inline.
On 7/21/15, 11:50 PM, "Yuchung Cheng" <ycheng@...gle.com> wrote:
>On Tue, Jul 21, 2015 at 9:21 PM, Lawrence Brakmo <brakmo@...com> wrote:
>> This is a request for comments.
>>
>> TCP-NV (New Vegas) is a major update to TCP-Vegas. An earlier version of
>> NV was presented at 2010's LPC (slides). It is a delayed based
>> congestion avoidance for the data center. This version has been tested
>> within a 10G rack where the HW RTTs are 20-50us.
>>
>> A description of TCP-NV, including implementation and experimental
>> results, can be found at:
>>
>>https://urldefense.proofpoint.com/v1/url?u=http://www.brakmo.org/networki
>>ng/tcp-nv/TCPNV.html&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=m30SgjN07T%2FK%2
>>FdV1ZIt1iA%3D%3D%0A&m=XeELWxnafKynbNgkHg6RW%2F85hv1bPWlufUn2Dh4cOH4%3D%0A
>>&s=0029c47e62d84d6ffd22bd33e1895a3f61eaa21d88cbfb553aa1df780bbbdcf9
>>
>> The current version includes many module parameters to support
>> experimentation with the parameters.
>>
>> Signed-off-by: Lawrence Brakmo <brakmo@...com>
>> ---
>> include/net/tcp.h | 1 +
>> net/ipv4/Kconfig | 16 ++
>> net/ipv4/Makefile | 1 +
>> net/ipv4/sysctl_net_ipv4.c | 9 +
>> net/ipv4/tcp_input.c | 2 +
>> net/ipv4/tcp_nv.c | 479
>>+++++++++++++++++++++++++++++++++++++++++++++
>> 6 files changed, 508 insertions(+)
>> create mode 100644 net/ipv4/tcp_nv.c
>>
>> diff --git a/include/net/tcp.h b/include/net/tcp.h
>> index 2e62efe..c0690ae 100644
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -281,6 +281,7 @@ extern unsigned int sysctl_tcp_notsent_lowat;
>> extern int sysctl_tcp_min_tso_segs;
>> extern int sysctl_tcp_autocorking;
>> extern int sysctl_tcp_invalid_ratelimit;
>> +extern int sysctl_tcp_nv_enable;
>>
>> extern atomic_long_t tcp_memory_allocated;
>> extern struct percpu_counter tcp_sockets_allocated;
>> diff --git a/net/ipv4/Kconfig b/net/ipv4/Kconfig
>> index 6fb3c90..c37b374 100644
>> --- a/net/ipv4/Kconfig
>> +++ b/net/ipv4/Kconfig
>> @@ -539,6 +539,22 @@ config TCP_CONG_VEGAS
>> window. TCP Vegas should provide less packet loss, but it is
>> not as aggressive as TCP Reno.
>>
>> +config TCP_CONG_NV
>> + tristate "TCP NV"
>> + default m
>> + ---help---
>> + TCP NV is a follow up to TCP Vegas. It has been modified to
>>deal with
>> + 10G networks, measurement noise introduced by LRO, GRO and
>>interrupt
>> + coalescence. In addition, it will decrease its cwnd
>>multiplicative
>multiplicatively
>
>> + instead of linearly.
>> +
>> + Note that in general congestion avoidance (cwnd decreased when
>># packets
>> + queued grows) cannot coexist with congestion control (cwnd
>>decreased only
>> + when there is packet loss) due to fairness issues. One scenario
>>when the
>s/the/they
>> + can coexist safely is when the CA flows have RTTs << CC flows
>>RTTs.
>> +
>> + For further details see
>>https://urldefense.proofpoint.com/v1/url?u=http://www.brakmo.org/networki
>>ng/tcp-nv/&k=ZVNjlDMF0FElm4dQtryO4A%3D%3D%0A&r=m30SgjN07T%2FK%2FdV1ZIt1iA
>>%3D%3D%0A&m=XeELWxnafKynbNgkHg6RW%2F85hv1bPWlufUn2Dh4cOH4%3D%0A&s=3441162
>>a0eefcad01003dbf0ba478e00a2080f76cd460eaf12213eb74f2eedbd
>> +
>> config TCP_CONG_SCALABLE
>> tristate "Scalable TCP"
>> default n
>> diff --git a/net/ipv4/Makefile b/net/ipv4/Makefile
>> index efc43f3..06f335f 100644
>> --- a/net/ipv4/Makefile
>> +++ b/net/ipv4/Makefile
>> @@ -50,6 +50,7 @@ obj-$(CONFIG_TCP_CONG_HSTCP) += tcp_highspeed.o
>> obj-$(CONFIG_TCP_CONG_HYBLA) += tcp_hybla.o
>> obj-$(CONFIG_TCP_CONG_HTCP) += tcp_htcp.o
>> obj-$(CONFIG_TCP_CONG_VEGAS) += tcp_vegas.o
>> +obj-$(CONFIG_TCP_CONG_NV) += tcp_nv.o
>> obj-$(CONFIG_TCP_CONG_VENO) += tcp_veno.o
>> obj-$(CONFIG_TCP_CONG_SCALABLE) += tcp_scalable.o
>> obj-$(CONFIG_TCP_CONG_LP) += tcp_lp.o
>> diff --git a/net/ipv4/sysctl_net_ipv4.c b/net/ipv4/sysctl_net_ipv4.c
>> index 433231c..31846d5 100644
>> --- a/net/ipv4/sysctl_net_ipv4.c
>> +++ b/net/ipv4/sysctl_net_ipv4.c
>> @@ -730,6 +730,15 @@ static struct ctl_table ipv4_table[] = {
>> .proc_handler = proc_dointvec_ms_jiffies,
>> },
>> {
>> + .procname = "tcp_nv_enable",
>> + .data = &sysctl_tcp_nv_enable,
>> + .maxlen = sizeof(int),
>> + .mode = 0644,
>> + .proc_handler = proc_dointvec_minmax,
>> + .extra1 = &zero,
>> + .extra2 = &one,
>> + },
>> + {
>> .procname = "icmp_msgs_per_sec",
>> .data = &sysctl_icmp_msgs_per_sec,
>> .maxlen = sizeof(int),
>> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
>> index aca4ae5..87560d9 100644
>> --- a/net/ipv4/tcp_input.c
>> +++ b/net/ipv4/tcp_input.c
>> @@ -101,6 +101,8 @@ int sysctl_tcp_thin_dupack __read_mostly;
>> int sysctl_tcp_moderate_rcvbuf __read_mostly = 1;
>> int sysctl_tcp_early_retrans __read_mostly = 3;
>> int sysctl_tcp_invalid_ratelimit __read_mostly = HZ/2;
>> +int sysctl_tcp_nv_enable __read_mostly = 1;
>> +EXPORT_SYMBOL(sysctl_tcp_nv_enable);
>>
>> #define FLAG_DATA 0x01 /* Incoming frame contained data.
>> */
>> #define FLAG_WIN_UPDATE 0x02 /* Incoming ACK was a
>>window update. */
>> diff --git a/net/ipv4/tcp_nv.c b/net/ipv4/tcp_nv.c
>> new file mode 100644
>> index 0000000..af451b6
>> --- /dev/null
>> +++ b/net/ipv4/tcp_nv.c
>> @@ -0,0 +1,479 @@
>> +/*
>> + * TCP NV: TCP with Congestion Avoidance
>> + *
>> + * TCP-NV is a successor of TCP-Vegas that has been developed to
>> + * deal with the issues that occur in modern networks.
>> + * Like TCP-Vegas, TCP-NV supports true congestion avoidance,
>> + * the ability to detect congestion before packet losses occur.
>> + * When congestion (queue buildup) starts to occur, TCP-NV
>> + * predicts what the cwnd size should be for the current
>> + * throughput and it reduces the cwnd proportionally to
>> + * the difference between the current cwnd and the predicted cwnd.
>> + * TCP-NV behaves like Reno when no congestion is detected, or when
>> + * recovering from packet losses.
>what happens when loss is not related to congestion?
This version makes no distinction. I will update a patch later (after I¹ve
done enough testing) that adds the option of not decreasing cwnd in some
cases (such as no congestion detected) as long as they are reasonable.
>> + *
>> + * TODO:
>> + * 1) Modify the behavior so cwnd can grow faster under certain
>>conditions
>> + * 2) Add mechanism to deal with reverse congestion.
>> + */
>> +
>> +#include <linux/mm.h>
>> +#include <linux/module.h>
>> +#include <linux/math64.h>
>> +#include <net/tcp.h>
>> +#include <linux/inet_diag.h>
>> +
>> +/* TCP NV parameters */
>> +static int nv_pad __read_mostly = 10;
>> +static int nv_pad_buffer __read_mostly = 2;
>> +static int nv_reset_period __read_mostly = 5;
>> +static int nv_min_cwnd = 10;
>> +static int nv_dec_eval_min_calls = 100;
>> +static int nv_ssthresh_eval_min_calls = 30;
>> +static int nv_rtt_min_cnt = 2;
>> +static int nv_cong_decrease_mult = 30*128/100;
>> +static int nv_ssthresh_factor = 8;
>> +static int nv_rtt_factor = 128;
>> +static int nv_rtt_cnt_dec_delta = 20; /* dec cwnd by this many RTTs */
>> +static int nv_dec_factor = 5; /* actual value is factor/8 */
>> +static int nv_loss_dec_factor = 820; /* on loss reduce cwnd by 20% */
>> +static int nv_cwnd_growth_factor = 2; /* larger => cwnd grows slower */
>> +
>> +module_param(nv_pad, int, 0644);
>> +MODULE_PARM_DESC(nv_pad, "extra packets above congestion level");
>> +module_param(nv_pad_buffer, int, 0644);
>> +MODULE_PARM_DESC(nv_pad_buffer, "no growth buffer zone");
>> +module_param(nv_reset_period, int, 0644);
>> +MODULE_PARM_DESC(nv_reset_period, "nv_min_rtt reset period (secs)");
>> +module_param(nv_min_cwnd, int, 0644);
>> +MODULE_PARM_DESC(nv_min_cwnd, "NV will not decrease cwnd below this
>>value"
>> + " without losses");
>> +module_param(nv_dec_eval_min_calls, int, 0644);
>> +MODULE_PARM_DESC(nv_dec_eval_min_calls, "Wait for this many data
>>points "
>> + "before declaring congestion (< 256)");
>> +module_param(nv_ssthresh_eval_min_calls, int, 0644);
>> +MODULE_PARM_DESC(nv_ssthresh_eval_min_calls, "Wait for this many data
>>points "
>> + "before declaring congestion during initial
>>slow-start");
>> +module_param(nv_rtt_min_cnt, int, 0644);
>> +MODULE_PARM_DESC(nv_rtt_min_cnt, "Wait for this many RTTs before
>>declaring"
>> + " congestion (<64)");
>> +module_param(nv_cong_decrease_mult, int, 0644);
>> +MODULE_PARM_DESC(nv_cong_decrease_mult, "Congestion decrease factor");
>> +module_param(nv_ssthresh_factor, int, 0644);
>> +MODULE_PARM_DESC(nv_ssthresh_factor, "ssthresh factor");
>> +module_param(nv_rtt_factor, int, 0644);
>> +MODULE_PARM_DESC(nv_rtt_factor, "rtt averaging factor (0-256)");
>> +module_param(nv_rtt_cnt_dec_delta, int, 0644);
>> +MODULE_PARM_DESC(nv_rtt_cnt_dec_delta, "decrease cwnd for this many
>>RTTs "
>> + "every 100 RTTs");
>> +module_param(nv_dec_factor, int, 0644);
>> +MODULE_PARM_DESC(nv_dec_factor, "decrease cwnd every ~192 RTTS by
>>factor/8");
>> +module_param(nv_loss_dec_factor, int, 0644);
>> +MODULE_PARM_DESC(nv_loss_dec_factor, "on loss new cwnd = cwnd * this /
>>1024");
>> +module_param(nv_cwnd_growth_factor, int, 0644);
>> +MODULE_PARM_DESC(nv_cwnd_growth_factor, "larger => cwnd grows slower");
>> +
>> +/* TCP NV Parameters */
>> +struct tcpnv {
>> + unsigned long nv_min_rtt_reset_jiffies; /* when to switch to
>> + * nv_min_rtt_new */
>> + u32 cnt; /* increase cwnd by 1 after ACKs */
>> + u32 loss_cwnd; /* cwnd at last loss */
>> + u8 nv_enable:1,
>> + nv_allow_cwnd_growth:1, /* whether cwnd can
>>grow */
>> + nv_rtt_cnt:6; /* RTTs without making ca decision */
>> + u8 nv_eval_call_cnt;/* call count since last eval */
>> + u8 nv_min_cwnd; /* nv won't make a ca decision if cwnd
>>is
>> + * smaller than this. It may grow to
>>handle
>> + * TSO, LRO and interrupt coalescence
>>because
>> + * with these a small cwnd cannot
>>saturate
>> + * the link. Note that this is
>>different from
>> + * sysctl_tcp_nv_min_cwnd */
>> + u8 available;
>> + u32 nv_last_rtt; /* last rtt */
>> + u32 nv_min_rtt; /* active min rtt. Used to determine
>>slope */
>> + u32 nv_min_rtt_new; /* min rtt for future use */
>> + u32 nv_rtt_max_rate; /* max rate seen during current RTT */
>> + u32 nv_rtt_start_seq; /* current RTT ends when packet arrives
>> + * acking beyond nv_rtt_start_seq */
>> + u32 nv_last_snd_una; /* Previous value of tp->snd_una. It is
>> + * used to determine bytes acked since
>>last
>> + * call to bictcp_acked */
>> + u32 nv_no_cong_cnt; /* Consecutive no congestion decisions
>>*/
>> + u32 nv_rtt_cnt_dec; /* RTTs since last temporary cwnd
>>decrease */
>> +};
>> +
>> +#define NV_INIT_RTT 0xffffffff
>> +#define NV_MIN_CWND 4
>> +#define NV_MIN_CWND_GROW 2
>> +#define NV_TSO_CWND_BOUND 80
>> +
>> +static inline void tcpnv_reset(struct tcpnv *ca, struct sock *sk)
>> +{
>> + struct tcp_sock *tp = tcp_sk(sk);
>> +
>> + ca->loss_cwnd = 0;
>> + ca->nv_no_cong_cnt = 0;
>> + ca->cnt = 0;
>> + ca->nv_rtt_cnt = 0;
>> + ca->nv_rtt_cnt_dec = 0;
>> + ca->nv_allow_cwnd_growth = 1;
>> + ca->nv_last_rtt = 0;
>> + ca->nv_rtt_max_rate = 0;
>> + ca->nv_rtt_start_seq = tp->snd_una;
>> + ca->nv_eval_call_cnt = 0;
>> + ca->nv_last_snd_una = tp->snd_una;
>> +}
>> +
>> +static void tcpnv_init(struct sock *sk)
>> +{
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + tcpnv_reset(ca, sk);
>> +
>> + ca->nv_min_rtt_reset_jiffies = jiffies + 2*HZ;
>> + ca->nv_min_rtt = NV_INIT_RTT;
>> + ca->nv_min_rtt_new = NV_INIT_RTT;
>> + ca->nv_enable = sysctl_tcp_nv_enable;
>> + ca->nv_min_cwnd = NV_MIN_CWND;
>> + if (nv_dec_eval_min_calls > 255)
>> + nv_dec_eval_min_calls = 255;
>> + if (nv_rtt_min_cnt > 63)
>> + nv_rtt_min_cnt = 63;
>> +}
>> +
>> +static void tcpnv_cong_avoid(struct sock *sk, u32 ack, u32 acked)
>> +{
>> + struct tcp_sock *tp = tcp_sk(sk);
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + if (!tcp_is_cwnd_limited(sk))
>> + return;
>> +
>> + /* Only grow cwnd if NV has not detected congestion */
>> + if (sysctl_tcp_nv_enable && ca->nv_enable &&
>> + !ca->nv_allow_cwnd_growth)
>> + return;
>> +
>> + if (tp->snd_cwnd <= tp->snd_ssthresh) {
>> + acked = tcp_slow_start(tp, acked);
>> + if (!acked)
>> + return;
>> + }
>> + if (ca->cnt == 0 || !(sysctl_tcp_nv_enable || ca->nv_enable))
>> + ca->cnt = tp->snd_cwnd;
>> +
>> + tcp_cong_avoid_ai(tp, ca->cnt, acked);
>> +}
>> +
>> +static u32 tcpnv_recalc_ssthresh(struct sock *sk)
>> +{
>> + const struct tcp_sock *tp = tcp_sk(sk);
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + ca->loss_cwnd = tp->snd_cwnd;
>> + return max((tp->snd_cwnd * nv_loss_dec_factor) >> 10, 2U);
>> +}
>> +
>> +static u32 tcpnv_undo_cwnd(struct sock *sk)
>> +{
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + return max(tcp_sk(sk)->snd_cwnd, ca->loss_cwnd);
>> +}
>> +
>> +static void tcpnv_state(struct sock *sk, u8 new_state)
>> +{
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + if (new_state == TCP_CA_Open) {
>> + ca->nv_enable = 1;
>> + tcpnv_reset(ca, sk);
>> + } else if (new_state == TCP_CA_Loss) {
>> + ca->nv_enable = 0;
>> + }
>> +}
>> +
>> +/* Do congestion avoidance calculaitons for TCP-NV
>> + */
>> +static void tcpnv_acked(struct sock *sk, struct ack_sample sample)
>> +{
>> + const struct inet_connection_sock *icsk = inet_csk(sk);
>> + struct tcp_sock *tp = tcp_sk(sk);
>> + struct tcpnv *ca = inet_csk_ca(sk);
>> + unsigned long now = jiffies;
>> + s64 rate64 = 0;
>> + u32 rate, max_win, cwnd_by_slope;
>> + u32 avg_rtt;
>> + u32 bytes_acked = 0;
>> +
>> + /* Some calls are for duplicates without timetamps */
>> + if (sample.rtt_us < 0)
>> + return;
>> +
>> + /* If not in TCP_CA_Open state, skip. */
>> + if (icsk->icsk_ca_state != TCP_CA_Open)
>> + return;
>> +
>> + /* If NV mode is not enabled, behave like Reno */
>> + if (!sysctl_tcp_nv_enable || !ca->nv_enable) {
>> + ca->nv_allow_cwnd_growth = 1;
>what's the use case of using NV with sysctl_tcp_nv_enable=0?
I¹m paranoid, this is to turn NV behavior off in case it starts acting
badly.
I¹ve done some testing within a rack, have plans to do more extensive
testing.
As per Neal¹s comment, I¹ve changed it to a module parameter making NV
even less
intrusive.
>
>> + return;
>> + }
>> +
>> + bytes_acked = tp->snd_una - ca->nv_last_snd_una;
>> + ca->nv_last_snd_una = tp->snd_una;
>> +
>> + if (sample.in_flight == 0)
>> + return;
>> +
>> + /* Calculate moving average of RTT */
>> + if (nv_rtt_factor > 0) {
>> + if (ca->nv_last_rtt > 0) {
>> + avg_rtt = (((u64)sample.rtt_us) * nv_rtt_factor
>>+
>> + ((u64)ca->nv_last_rtt)
>> + * (256 - nv_rtt_factor)) >> 8;
>> + } else {
>> + avg_rtt = sample.rtt_us;
>> + ca->nv_min_rtt = avg_rtt << 1;
>> + }
>> + ca->nv_last_rtt = avg_rtt;
>> + } else {
>> + avg_rtt = sample.rtt_us;
>> + }
>> +
>> + /* rate in 100's bits per second */
>> + rate64 = ((u64)sample.in_flight) * 8000000;
>> + rate = (u32)div64_u64(rate64, (u64)(avg_rtt*100));
>> +
>> + /* Remember the maximum rate seen during this RTT
>> + * Note: It may be more than one RTT. This function should be
>> + * called at least nv_dec_eval_min_calls times.
>> + */
>> + if (ca->nv_rtt_max_rate < rate)
>> + ca->nv_rtt_max_rate = rate;
>> +
>> + /* We have valid information, increment counter */
>> + if (ca->nv_eval_call_cnt < 255)
>> + ca->nv_eval_call_cnt++;
>> +
>> + /* update min rtt if necessary */
>> + if (avg_rtt < ca->nv_min_rtt)
>> + ca->nv_min_rtt = avg_rtt;
>> +
>> + /* update future min_rtt if necessary */
>> + if (avg_rtt < ca->nv_min_rtt_new)
>> + ca->nv_min_rtt_new = avg_rtt;
>> +
>> + /* nv_min_rtt is updated with the minimum (possibley averaged)
>>rtt
>> + * seen in the last sysctl_tcp_nv_reset_period seconds (i.e. a
>> + * warm reset). This new nv_min_rtt will be continued to be
>>updated
>> + * and be used for another sysctl_tcp_nv_reset_period seconds,
>> + * when it will be updated again.
>> + * In practice we introduce some randomness, so the actual
>>period used
>> + * is chosen randomly from the range:
>> + * [sysctl_tcp_nv_reset_period*3/4,
>>sysctl_tcp_nv_reset_period*5/4)
>> + */
>> + if (time_after_eq(now, ca->nv_min_rtt_reset_jiffies)) {
>> + unsigned char rand;
>> + ca->nv_min_rtt = ca->nv_min_rtt_new;
>> + ca->nv_min_rtt_new = NV_INIT_RTT;
>> + get_random_bytes(&rand, 1);
>> + ca->nv_min_rtt_reset_jiffies =
>> + now + ((nv_reset_period*(384 + rand)*HZ)>>9);
>> + /* Every so often we decrease nv_min_cwnd in case
>>previous
>> + * value is no longer accurate.
>> + */
>> + ca->nv_min_cwnd = max(ca->nv_min_cwnd/2, NV_MIN_CWND);
>> + }
>> +
>> + /* Once per RTT check if we need to do congestion avoidance */
>> + if (before(ca->nv_rtt_start_seq, tp->snd_una)) {
>> + ca->nv_rtt_start_seq = tp->snd_nxt;
>> + if (ca->nv_rtt_cnt < 63)
>> + /* Increase counter for RTTs without CA
>>decision */
>> + ca->nv_rtt_cnt++;
>> + if (ca->nv_rtt_cnt_dec < 255)
>> + /* Increase counter for temporary cwnd decrease
>>*/
>> + ca->nv_rtt_cnt_dec++;
>> +
>> + /* If this function is only called once within an RTT
>> + * the cwnd is probably too small (in some cases due to
>> + * tso, lro or interrupt coalescence), so we increase
>> + * nv_min_cwnd.
>> + */
>> + if (ca->nv_eval_call_cnt == 1
>> + && bytes_acked >= (ca->nv_min_cwnd - 1) *
>>tp->mss_cache
>> + && ca->nv_min_cwnd < (NV_TSO_CWND_BOUND + 1)
>> + && ca->nv_rtt_cnt_dec < 192) {
>> + ca->nv_min_cwnd = min(ca->nv_min_cwnd
>> + + NV_MIN_CWND_GROW,
>> + NV_TSO_CWND_BOUND + 1);
>> + ca->nv_rtt_start_seq = tp->snd_nxt +
>> + ca->nv_min_cwnd*tp->mss_cache;
>> + ca->nv_eval_call_cnt = 0;
>> + ca->nv_allow_cwnd_growth = 1;
>> + return;
>> + }
>> +
>> + /* Every 192 to 320 RTTs decrease cwnd to get better
>>min RTT
>> + * measurement. In practice we accomplish this by
>>initializing
>> + * nv_rtt_cnd_dec randomly form the range [0, 128) and
>> + * stopping at 320.
>> + * We keep the value low for nv_rtt_cnt_dec_delta RTTs
>>and then
>> + * we restore cwnd to its previous value (by setting
>> + * ssthresh to the previous value).
>> + */
>> + if (ca->nv_rtt_cnt_dec == 320) {
>> + /* decrease cwnd and ssthresh */
>> + tp->snd_cwnd =
>> + max((unsigned int)nv_min_cwnd,
>> + ((tp->snd_cwnd * nv_dec_factor) >>
>>3));
>> + tp->snd_ssthresh =
>> + max(tp->snd_cwnd,
>> + ((tp->snd_ssthresh * nv_dec_factor)
>>>> 3));
>> + ca->nv_allow_cwnd_growth = 0;
>> + return;
>> + } else if (ca->nv_rtt_cnt_dec > 320) {
>> + if (ca->nv_rtt_cnt_dec - 320 >=
>>nv_rtt_cnt_dec_delta) {
>> + /* Restore ssthresh to restore cwnd */
>> + unsigned char rand;
>> + get_random_bytes(&rand, 1);
>> + ca->nv_rtt_cnt_dec = rand >> 1;
>> + tp->snd_ssthresh = (tp->snd_ssthresh <<
>>3)
>> + / nv_dec_factor;
>> + ca->nv_allow_cwnd_growth = 1;
>> + ca->nv_no_cong_cnt = 0;
>> + }
>> + return;
>> + }
>> +
>> + /* Find the ideal cwnd for current rate from slope
>> + * slope = 80000.0 * mss / nv_min_rtt
>> + * cwnd_by_slope = nv_rtt_max_rate / slope
>> + */
>> + cwnd_by_slope = (u32)
>> + div64_u64(((u64)ca->nv_rtt_max_rate) *
>>ca->nv_min_rtt,
>> + (u64)(80000 * tp->mss_cache));
>> + max_win = cwnd_by_slope + nv_pad;
>> +
>> + /* If cwnd > max_win, decrease cwnd
>> + * if cwnd < max_win, grow cwnd
>> + * else leave the same
>> + */
>> + if (tp->snd_cwnd > max_win) {
>> + /* there is congestion, check that it is ok
>> + * to make a CA decision
>> + * 1. We should have at least
>>nv_dec_eval_min_calls
>> + * data points before making a CA decision
>> + * 2. We only make a congesion decision after
>> + * nv_rtt_min_cnt RTTs
>> + */
>> + if (ca->nv_rtt_cnt < nv_rtt_min_cnt)
>> + return;
>> + else if (tp->snd_ssthresh ==
>>TCP_INFINITE_SSTHRESH) {
>> + if (ca->nv_eval_call_cnt <
>> + nv_ssthresh_eval_min_calls)
>> + return;
>> + } else if (ca->nv_eval_call_cnt <
>> + nv_dec_eval_min_calls) {
>> + return;
>> + }
>> +
>> + /* We have enough data to determine we are
>>congested */
>> + ca->nv_allow_cwnd_growth = 0;
>> + tp->snd_ssthresh =
>> + (nv_ssthresh_factor * max_win) >> 3;
>> + if (tp->snd_cwnd - max_win > 2) {
>> + /* gap > 2, we do exponential cwnd
>>decrease */
>> + int dec;
>> + dec = max(2U, ((tp->snd_cwnd - max_win)
>>*
>> + nv_cong_decrease_mult)
>>>> 7);
>> + tp->snd_cwnd -= dec;
>> + } else if (nv_cong_decrease_mult > 0) {
>> + tp->snd_cwnd = max_win;
>> + }
>> + ca->cnt = tp->snd_cwnd;
>> + ca->nv_no_cong_cnt = 0;
>> + } else if (tp->snd_cwnd <= max_win - nv_pad_buffer) {
>> + /* We allow growth of cwnd every RTT since we
>>would
>> + * have grown even if we waited (just slower)
>> + */
>> + ca->nv_allow_cwnd_growth = 1;
>> + ca->nv_no_cong_cnt++;
>> + if (nv_cwnd_growth_factor > 0 &&
>> + ca->nv_no_cong_cnt > nv_cwnd_growth_factor)
>>{
>> + ca->cnt = max(ca->cnt >> 1, (u32) 4);
>> + ca->nv_no_cong_cnt = 0;
>> + }
>> + } else {
>> + ca->nv_allow_cwnd_growth = 0;
>> + }
>> +
>> + /* update state */
>> + ca->nv_eval_call_cnt = 0;
>> + ca->nv_rtt_cnt = 0;
>> + ca->nv_rtt_max_rate = 0;
>> +
>> + /* Don't want to make cwnd < nv_min_cwnd
>> + * (it wasn't before, if it is now is because nv
>> + * decreased it).
>> + */
>> + if (tp->snd_cwnd < nv_min_cwnd)
>> + tp->snd_cwnd = nv_min_cwnd;
>> +
>> + }
>> +}
>> +
>> +/* Extract info for Tcp socket info provided via netlink */
>> +size_t tcpnv_get_info(struct sock *sk, u32 ext, int *attr,
>> + union tcp_cc_info *info)
>> +{
>> + const struct tcpnv *ca = inet_csk_ca(sk);
>> +
>> + if (ext & (1 << (INET_DIAG_VEGASINFO - 1))) {
>> + info->vegas.tcpv_enabled = ca->nv_enable
>> + && sysctl_tcp_nv_enable;
>> + info->vegas.tcpv_rttcnt = ca->nv_rtt_cnt;
>> + info->vegas.tcpv_rtt = ca->nv_last_rtt;
>> + info->vegas.tcpv_minrtt = ca->nv_min_rtt;
>> +
>> + *attr = INET_DIAG_VEGASINFO;
>> + return sizeof(struct tcpvegas_info);
>> + }
>> + return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(tcpnv_get_info);
>> +
>> +static struct tcp_congestion_ops tcpnv __read_mostly = {
>> + .init = tcpnv_init,
>> + .ssthresh = tcpnv_recalc_ssthresh,
>> + .cong_avoid = tcpnv_cong_avoid,
>> + .set_state = tcpnv_state,
>> + .undo_cwnd = tcpnv_undo_cwnd,
>> + .pkts_acked = tcpnv_acked,
>> + .get_info = tcpnv_get_info,
>> +
>> + .owner = THIS_MODULE,
>> + .name = "nv",
>> +};
>> +
>> +static int __init tcpnv_register(void)
>> +{
>> + BUILD_BUG_ON(sizeof(struct tcpnv) > ICSK_CA_PRIV_SIZE);
>> +
>> + return tcp_register_congestion_control(&tcpnv);
>> +}
>> +
>> +static void __exit tcpnv_unregister(void)
>> +{
>> + tcp_unregister_congestion_control(&tcpnv);
>> +}
>> +
>> +module_init(tcpnv_register);
>> +module_exit(tcpnv_unregister);
>> +
>> +MODULE_AUTHOR("Lawrence Brakmo");
>> +MODULE_LICENSE("GPL");
>> +MODULE_DESCRIPTION("TCP NV");
>> +MODULE_VERSION("1.0");
>> --
>> 1.8.1
>>
>> --
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