From: Frédéric Lécaille <flecaille@haproxy.com>
Date: Thu, 30 Mar 2023 13:31:06 +0000 (+0200)
Subject: BUG/MINOR: quic: Wrong rtt variance computing
X-Git-Tag: v2.8-dev7~124
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=5d5afe790016401952117dbaff8a3324260faf8e;p=thirdparty%2Fhaproxy.git

BUG/MINOR: quic: Wrong rtt variance computing

In ->srtt quic_loss struct this is 8*srtt which is stored so that not to have to multiply/devide
it to compute the RTT variance (at least). This is where there was a bug in quic_loss_srtt_update():
each time ->srtt must be used, it must be devided by 8 or right shifted by 3.
This bug had a very bad impact for network with non negligeable packet loss.

Must be backported to 2.6 and 2.7.
---

diff --git a/src/quic_loss.c b/src/quic_loss.c
index 8f19645a70..eff8e6c36c 100644
--- a/src/quic_loss.c
+++ b/src/quic_loss.c
@@ -37,7 +37,7 @@ void quic_loss_srtt_update(struct quic_loss *ql,
 		/* Specific to QUIC (RTT adjustment). */
 		if (ack_delay && rtt > ql->rtt_min + ack_delay)
 			rtt -= ack_delay;
-		diff = ql->srtt - rtt;
+		diff = (ql->srtt >> 3) - rtt;
 		if (diff < 0)
 			diff = -diff;
 		/* 4*rttvar = 3*rttvar + |diff| */