On Wed, Aug 5, 2015 at 3:39 AM, Lawrence Brakmo <bra...@fb.com> wrote:
> This is a request for comments.
Nice to see more development on delay-based congestion control.
It would be good to see how NV stacks up against CDG. Any chance of
adding cdg as a congestion control parameter to your experiments?
Experiments on NV without its temporary cwnd reductions would also be
of interest -- to get a reference of how effective this mechanism is.
> +#define NV_INIT_RTT 0xffffffff
Maybe use U32_MAX?
> +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 = nv_enable;
Can this assignment be ca->nv_enable = 1? That would match the
TCP_CA_Open case in tcpnv_state().
> + if (nv_dec_eval_min_calls > 255)
> + nv_dec_eval_min_calls = 255;
> + if (nv_rtt_min_cnt > 63)
> + nv_rtt_min_cnt = 63;
nv_dec_eval_min_calls can be clamped to 0-255 by changing its type to u8.
nv_rtt_min_cnt can also be u8? In struct tcpnv, perhaps move
nv_rtt_cnt to the available byte.
> +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 (nv_enable && ca->nv_enable && !ca->nv_allow_cwnd_growth)
> + return;
The check for ca->nv_enable might be overly harsh on some unfortunate
sockets in TCP_CA_Disorder. Is it needed here?
> +static void tcpnv_acked(struct sock *sk, struct ack_sample *sample)
Maybe move some of this function to tcpnv_cong_avoid()?
> +{
> + 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;
Consider using samples in other states too, especially
TCP_CA_Disorder. Linux 4.2 enhances RTT sampling from SACKs, so any
non-negative RTT sample should be fully usable.
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