Re: [PATCH/RFC] [v2] TCP: use non-delayed ACK for congestion control RTT
From: Ilpo Järvinen <hidden>
Date: 2007-12-21 14:07:34
On Fri, 21 Dec 2007, Gavin McCullagh wrote:
On Fri, 21 Dec 2007, David Miller wrote:quoted
When Gavin respins the patch I'll look at in the context of submitting it as a bug fix. So Gavin please generate the patch against Linus's vanilla GIT tree or net-2.6, your choise.The existing patch was against Linus' linux-2.6.git from a few days ago so I've updated my tree and regenerated the patch (below). Is that the right one? I'm just checking through the existing CA modules. I don't see the rtt used for RTO anywhere. This is what I gather they're each using rtt for.
I meant more timeout like fashion (e.g., to "timeout" some internal phase but I don't find that too likely)... Thanks for checking them.
So as far as I can tell, timeout stuff is not ever altered using pkts_acked() so I guess this fix only affects westwood, htcp and cubic just now. I need to re-read properly, but I think the same problem affects the microsecond values where TCP_CONG_RTT_STAMP is set (used by vegas, veno, yeah, illinois). I might follow up with another patch which changes the behaviour where TCP_CONG_RTT_STAMP when I'm more sure of that.
Please do, you might have to remove fully_acked checks to do that right though so it won't be as straight-forward change as this one and requires some amount of thinking to result in a right thing.
quoted hunk ↗ jump to hunk
Signed-off-by: Gavin McCullagh <redacted>diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 889c893..6fb7989 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c@@ -2651,6 +2651,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p, u32 cnt = 0; u32 reord = tp->packets_out; s32 seq_rtt = -1; + s32 ca_seq_rtt = -1; ktime_t last_ackt = net_invalid_timestamp(); while ((skb = tcp_write_queue_head(sk)) && skb != tcp_send_head(sk)) {@@ -2686,13 +2687,15 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p, if (sacked & TCPCB_SACKED_RETRANS) tp->retrans_out -= packets_acked; flag |= FLAG_RETRANS_DATA_ACKED; + ca_seq_rtt = -1; seq_rtt = -1; if ((flag & FLAG_DATA_ACKED) || (packets_acked > 1)) flag |= FLAG_NONHEAD_RETRANS_ACKED; } else { + ca_seq_rtt = now - scb->when; if (seq_rtt < 0) { - seq_rtt = now - scb->when; + seq_rtt = ca_seq_rtt; if (fully_acked) last_ackt = skb->tstamp; }@@ -2709,8 +2712,9 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p, !before(end_seq, tp->snd_up)) tp->urg_mode = 0; } else { + ca_seq_rtt = now - scb->when; if (seq_rtt < 0) { - seq_rtt = now - scb->when; + seq_rtt = ca_seq_rtt; if (fully_acked) last_ackt = skb->tstamp; }@@ -2772,8 +2776,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, s32 *seq_rtt_p, net_invalid_timestamp())) rtt_us = ktime_us_delta(ktime_get_real(), last_ackt); - else if (seq_rtt > 0) - rtt_us = jiffies_to_usecs(seq_rtt); + else if (ca_seq_rtt > 0) + rtt_us = jiffies_to_usecs(ca_seq_rtt); } ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
Acked-by: Ilpo Järvinen <redacted> / Reviewed-by... whatever, I don't know if they really started to use it or not... :-) -- i.