[Bloat] Why you need at least 3Mbps upload to get good game performance with ~1500byte packets: Doing the math

[Sebastian Moeller]

Hi Toke,


> On Dec 9, 2020, at 11:52, Toke Høiland-Jørgensen via Bloat <bloat at lists.bufferbloat.net> wrote:
> 
> Kenneth Porter <shiva at sewingwitch.com> writes:
> 
>> <https://forum.openwrt.org/t/why-you-need-at-least-3mbps-upload-to-get-good-game-performance-with-1500byte-packets-doing-the-math/81240>
>> 
>> Upstream article:
>> 
>> <http://models.street-artists.org/2020/12/05/why-gaming-on-a-dsl-line-is-terrible-and-the-math-says-theres-nothing-you-can-do-about-it/>
> 
> Good points, but doesn't mention options to decrease the packet size
> (lower MTU/MSS clamping)... :)

	But he is doing exactly that in the script he developed for OpenWrt games on poor links:

https://github.com/dlakelan/routerperf/blob/master/SimpleHFSCgamerscript.sh


    iptables -t mangle -F FORWARD # to flush the openwrt default MSS clamping rule
    if [ $UPRATE -lt 3000 ]; then
	ipt64 -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o $LAN -j TCPMSS --set-mss 540
    fi
    if [ $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
	ipt64 -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN -o $WAN -j TCPMSS --set-mss 540
    fi


We are actually trying to get something along that lines packaged as a script for sqm-scripts, but that is delayed since I need to fix some iptables stuff that seems to not work anymore first....


> 
> -Toke
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