From: Eric Dumazet <eric.dumazet@gmail.com>
To: LovelyLich <lovelylich@gmail.com>, Yuchung Cheng <ycheng@google.com>
Cc: netdev@vger.kernel.org
Subject: Re: Why we discard all rtt samples when only some of the acked skbs have been retransmited in processing ack?
Date: Mon, 16 Sep 2013 22:11:22 -0700 [thread overview]
Message-ID: <1379394682.29845.2.camel@edumazet-glaptop> (raw)
In-Reply-To: <CAAA3+BpsxtyM2uAvX6B4ys73ZC6fX5K1ib3Acsk0fp5cQBNgWg@mail.gmail.com>
On Tue, 2013-09-17 at 12:01 +0800, LovelyLich wrote:
> Hi Eric,
>
> In tcp_clean_rtx_queue(), we set the flag FLAG_RETRANS_DATA_ACKED when we
>
> encounter one ever retransmited skb A. But if there is one( or more) skb B
>
> after this retransmited skb, and we calculate the rtt for skb B. The question
>
> is because we have set the flag FLAG_RETRANS_DATA_ACKED, and we will just
>
> return in tcp_ack_no_tstamp() !
>
> Two questions:
>
> 1. if we will just ignore all packets in this ack, we do not need to calculate
>
> skb B's rtt sample.
>
> 2. what I want to know, even if A's rtt sample is not reliable, but B's rtt
>
> sample can be trusted. Why we discard it ?
>
>
>
> Thanks in advanced.
>
Good point !
Yuchung, what do you think of following patch ?
diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 25a89ea..7f12b96 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2971,7 +2971,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
struct sk_buff *skb;
u32 now = tcp_time_stamp;
int fully_acked = true;
- int flag = 0;
+ int flag = FLAG_RETRANS_DATA_ACKED;
u32 pkts_acked = 0;
u32 reord = tp->packets_out;
u32 prior_sacked = tp->sacked_out;
@@ -3002,7 +3002,6 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
if (sacked & TCPCB_RETRANS) {
if (sacked & TCPCB_SACKED_RETRANS)
tp->retrans_out -= acked_pcount;
- flag |= FLAG_RETRANS_DATA_ACKED;
} else {
ca_seq_rtt = now - scb->when;
last_ackt = skb->tstamp;
@@ -3013,6 +3012,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
reord = min(pkts_acked, reord);
if (!after(scb->end_seq, tp->high_seq))
flag |= FLAG_ORIG_SACK_ACKED;
+ flag &= ~FLAG_RETRANS_DATA_ACKED;
}
if (sacked & TCPCB_SACKED_ACKED)
next prev parent reply other threads:[~2013-09-17 5:11 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-17 4:01 Why we discard all rtt samples when only some of the acked skbs have been retransmited in processing ack? LovelyLich
2013-09-17 5:11 ` Eric Dumazet [this message]
2013-09-17 13:31 ` Neal Cardwell
2013-09-17 14:53 ` Yuchung Cheng
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