From: John Heffner <jheffner@psc.edu>
To: John Heffner <jheffner@psc.edu>
Cc: Stephen Hemminger <shemminger@osdl.org>,
David Miller <davem@davemloft.net>,
netdev <netdev@vger.kernel.org>
Subject: Re: simplify microsecond rtt sampling
Date: Wed, 27 Sep 2006 16:13:29 +0100 [thread overview]
Message-ID: <451A9519.6000504@psc.edu> (raw)
In-Reply-To: <451A5EC9.6090001@psc.edu>
Okay, this patch is junk (never trust compile-tested code). Will send
something better soon.
-John
John Heffner wrote:
> About commit 2d2abbab63f6726a147ae61ada39bf2c9ee0db9a:
>
> It looks like this patch bypassed the enforcement of Karn's algorithm in
> tcp_ack_no_tstamp() for the purposes of usec RTT sampling used by
> congestion control modules. This will give them bad RTT data when there
> are retransmits. I haven't actually observed this, but it seems like it
> would be the case. ;) Please correct me if I'm wrong.
>
> Here's a patch that should be a fix.
>
>
>
> Signed-off-by: John Heffner <jheffner@psc.edu>
>
>
> ------------------------------------------------------------------------
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 159fa3f..725c868 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -2306,8 +2306,6 @@ static int tcp_clean_rtx_queue(struct so
> seq_rtt = -1;
> } else if (seq_rtt < 0) {
> seq_rtt = now - scb->when;
> - if (rtt_sample)
> - (*rtt_sample)(sk, tcp_usrtt(skb));
> }
> if (sacked & TCPCB_SACKED_ACKED)
> tp->sacked_out -= tcp_skb_pcount(skb);
> @@ -2320,8 +2318,6 @@ static int tcp_clean_rtx_queue(struct so
> }
> } else if (seq_rtt < 0) {
> seq_rtt = now - scb->when;
> - if (rtt_sample)
> - (*rtt_sample)(sk, tcp_usrtt(skb));
> }
> tcp_dec_pcount_approx(&tp->fackets_out, skb);
> tcp_packets_out_dec(tp, skb);
> @@ -2333,6 +2329,8 @@ static int tcp_clean_rtx_queue(struct so
> if (acked&FLAG_ACKED) {
> tcp_ack_update_rtt(sk, acked, seq_rtt);
> tcp_ack_packets_out(sk, tp);
> + if (rtt_sample && !(acked & FLAG_RETRANS_DATA_ACKED))
> + (*rtt_sample)(sk, tcp_usrtt(skb));
>
> if (icsk->icsk_ca_ops->pkts_acked)
> icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
next prev parent reply other threads:[~2006-09-27 15:13 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-09-27 11:21 simplify microsecond rtt sampling John Heffner
2006-09-27 15:13 ` John Heffner [this message]
2006-09-28 12:35 ` John Heffner
2006-09-28 12:47 ` John Heffner
2006-09-28 16:36 ` Stephen Hemminger
2006-09-28 21:49 ` David Miller
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