Hi All... In working with @knomax and thinking about the issues in this thread: Why you need at least 3Mbps upload to get good game performance: Doing the math
We came up with the following adjustments to this public script which do two important things:
-
For connections less than 3Mbps it changes the OpenWrt firewall to use MSS clamping to 540 byte packets each direction. This causes TCP streams to be much less efficient, but the packets being sent take about 1/3 of the time, thereby limiting jitter, which we assume is more important to the audience reading this thread
-
When the connection is asymmetric, so that upload/download > 5 it uses a rate-limiter on sending small ACKs on the WAN, it allows 100 acks/second with a 100 packet burst, and drops 90% of acks over that randomly. This seems to make a HUGE difference with asymmetry... cake does something probably smarter than this, but this should work well.
New script:
#!/bin/sh
## "atm" for old-school DSL or change to "DOCSIS" for cable modem, or "other" for everything else
LINKTYPE="ethernet"
WAN=veth0 # change this to your WAN device name
UPRATE=18000 #change this to your kbps upload speed
LAN=veth1
DOWNRATE=65000 #change this to about 80% of your download speed (in kbps)
## how many kbps of UDP upload and download do you need for your games
## across all gaming machines?
GAMEUP=800
GAMEDOWN=1600
## set this to "red" or if you want to differentiate between game
## packets into 3 different classes you can use either "drr" or "qfq"
## be aware not all machines will have drr or qfq available
## also qfq or drr require setting up tc filters!
gameqdisc="red"
GAMINGIP="192.168.1.111" ## change this
cat <<EOF
This script prioritizes the UDP packets from / to a set of gaming
machines into a real-time HFSC queue with guaranteed total bandwidth
Based on your settings:
Game upload guarantee = $GAMEUP kbps
Game download guarantee = $GAMEDOWN kbps
Download direction only works if you install this on a *wired* router
and there is a separate AP wired into your network, because otherwise
there are multiple parallel queues for traffic to leave your router
heading to the LAN.
Based on your link total bandwidth, the **minimum** amount of jitter
you should expect in your network is about:
UP = $(((1500*8)*3/UPRATE)) ms
DOWN = $(((1500*8)*3/DOWNRATE)) ms
In order to get lower minimum jitter you must upgrade the speed of
your link, no queuing system can help.
Please note for your display rate that:
at 30Hz, one on screen frame lasts: 33.3 ms
at 60Hz, one on screen frame lasts: 16.6 ms
at 144Hz, one on screen frame lasts: 6.9 ms
This means the typical gamer is sensitive to as little as on the order
of 5ms of jitter. To get 5ms minimum jitter you should have bandwidth
in each direction of at least:
$((1500*8*3/5)) kbps
The queue system can ONLY control bandwidth and jitter in the link
between your router and the VERY FIRST device in the ISP
network. Typically you will have 5 to 10 devices between your router
and your gaming server, any of those can have variable delay and ruin
your gaming, and there is NOTHING that your router can do about it.
EOF
setqdisc () {
DEV=$1
RATE=$2
OH=37
MTU=1500
highrate=$((RATE*90/100))
lowrate=$((RATE*10/100))
gamerate=$3
useqdisc=$4
tc qdisc del dev "$DEV" root
case $LINKTYPE in
"atm")
tc qdisc replace dev "$DEV" handle 1: root stab mtu 2047 tsize 512 mpu 68 overhead ${OH} linklayer atm hfsc default 3
;;
"DOCSIS")
tc qdisc replace dev $DEV stab overhead 25 linklayer ethernet handle 1: root hfsc default 3
;;
*)
tc qdisc replace dev $DEV stab overhead 40 linklayer ethernet handle 1: root hfsc default 3
;;
esac
#limit the link overall:
tc class add dev "$DEV" parent 1: classid 1:1 hfsc ls m2 "${RATE}kbit" ul m2 "${RATE}kbit"
# high prio realtime class
tc class add dev "$DEV" parent 1:1 classid 1:2 hfsc rt m1 "${highrate}kbit" d 80ms m2 "${gamerate}kbit"
# other prio class
tc class add dev "$DEV" parent 1:1 classid 1:3 hfsc ls m1 "${lowrate}kbit" d 80ms m2 "${highrate}kbit"
## set this to "drr" or "qfq" to differentiate between different game
## packets, or use "pfifo" to treat all game packets equally
REDMIN=$((gamerate*30/8)) #30 ms of data
if [ $REDMIN -lt 3000 ]; then
REDMIN=3000
fi
REDMAX=$((REDMIN * 4)) #200ms of data
case $useqdisc in
"drr")
tc qdisc add dev "$DEV" parent 1:2 handle 2:0 drr
tc class add dev "$DEV" parent 2:0 classid 2:1 drr quantum 8000
tc qdisc add dev "$DEV" parent 2:1 handle 10: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
tc class add dev "$DEV" parent 2:0 classid 2:2 drr quantum 4000
tc qdisc add dev "$DEV" parent 2:2 handle 20: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
tc class add dev "$DEV" parent 2:0 classid 2:3 drr quantum 1000
tc qdisc add dev "$DEV" parent 2:3 handle 30: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
## with this send high priority game packets to 10:, medium to 20:, normal to 30:
## games will not starve but be given relative importance based on the quantum parameter
;;
"qfq")
tc qdisc add dev "$DEV" parent 1:2 handle 2:0 qfq
tc class add dev "$DEV" parent 2:0 classid 2:1 qfq weight 8000
tc qdisc add dev "$DEV" parent 2:1 handle 10: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
tc class add dev "$DEV" parent 2:0 classid 2:2 qfq weight 4000
tc qdisc add dev "$DEV" parent 2:2 handle 20: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
tc class add dev "$DEV" parent 2:0 classid 2:3 qfq weight 1000
tc qdisc add dev "$DEV" parent 2:3 handle 30: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
## with this send high priority game packets to 10:, medium to 20:, normal to 30:
## games will not starve but be given relative importance based on the weight parameter
;;
*)
tc qdisc add dev "$DEV" parent 1:2 handle 10: red limit 150000 min $REDMIN max $REDMAX avpkt 500 bandwidth ${RATE}kbit probability 1.0
## send game packets to 10:, they're all treated the same
;;
esac
if [ $((MTU * 8 * 10 / RATE > 50)) -eq 1 ]; then ## if one MTU packet takes more than 5ms
echo "adding PIE qdisc for non-game traffic due to slow link"
tc qdisc add dev "$DEV" parent 1:3 handle 3: pie limit $((RATE * 200 / (MTU * 8))) target 80ms ecn tupdate 40ms bytemode
else ## we can have queues with multiple packets without major delays, fair queuing is more meaningful
echo "adding fq_codel qdisc for non-game traffic due to fast link"
tc qdisc add dev "$DEV" parent 1:3 handle 3: fq_codel limit $((RATE * 200 / (MTU * 8))) quantum $((MTU * 2))
fi
}
setqdisc $WAN $UPRATE $GAMEUP $gameqdisc
## uncomment this to do the download direction via output of LAN
setqdisc $LAN $DOWNRATE $GAMEDOWN $gameqdisc
## we want to classify packets, so use these rules
cat <<EOF
We are going to add classification rules via iptables to the
POSTROUTING chain. You should actually read and ensure that these
rules make sense in your firewall before running this script.
Continue? (type y or n and then RETURN/ENTER)
EOF
read -r cont
if [ "$cont" = "y" ]; then
iptables -t mangle -F POSTROUTING
iptables -t mangle -A POSTROUTING -j CLASSIFY --set-class 1:3 # default everything to 1:3, the "non-game" qdisc
if [ "$gameqdisc" = "red" ]; then
iptables -t mangle -A POSTROUTING -p udp -s ${GAMINGIP} -j CLASSIFY --set-class 1:2
iptables -t mangle -A POSTROUTING -p udp -d ${GAMINGIP} -j CLASSIFY --set-class 1:2
else
echo "YOU MUST PLACE CLASSIFIERS FOR YOUR GAME TRAFFIC HERE"
echo "SEND TRAFFIC TO 2:1 (high) or 2:2 (medium) or 3:3 (normal)"
fi
if [ $((UPRATE/DOWNRATE > 5)) -eq 1 ]; then
## we need to trim acks in the upstream direction, we let 100/second through, and then drop 90% of the rest
iptables -A forwarding_rule -p tcp -m tcp --tcp-flags ACK ACK -o $WAN -m length --length 0:100 -m limit --limit 100/second --limit-burst 100
iptables -A forwarding_rule -p tcp -m tcp --tcp-flags ACK ACK -o $WAN -m length --length 0:100 -m statistic --mode random --probability .90 -j DROP
fi
if [$UPRATE -lt 3000 -o $DOWNRATE -lt 3000 ]; then
## need to clamp MSS to 540 bytes in both directions to reduce
## the latency increase caused by 1 packet ahead of us in the
## queue since rates are too low to send 1500 byte packets at acceptable delay
iptables -t mangle -F FORWARD # to flush the openwrt default MSS clamping rule
iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o $WAN -j TCPMSS --set-mss 540
iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o $LAN -j TCPMSS --set-mss 540
fi
else
cat <<EOF
Check the rules and come back when you're ready.
EOF
fi
echo "DONE!"
if [ $qdisc = "red" ]; then
echo "Can not output tc -s qdisc because it crashes on OpenWrt when using RED qdisc, but things are working!"
else
tc -s qdisc
fi