[Bloat] Best practices for paced TCP on Linux?

Dave Taht dave.taht at gmail.com
Sat Apr 7 11:50:24 PDT 2012

Steinar: Judging from these results it sounds like you should try
limiting the send window.

I don't know what the right number is, or what the current calculation
for what percentage
of this is used for window related buffering, (anyone?) but reducing
the defaults by a lot for your tcp based video servers seems
like a good idea.

to do that, edit /etc/sysctl.conf, add or change the line for

net.core.wmem_max = 256000 # or less. or more. 5Mbit stream...fairly
short rtts... hmm.. no brain cells. no sleep. ?

This is another parameter that may apply, the last value should be changed.

net.ipv4.tcp_wmem = 4096 65536 2097152

These of course change it globally. you commit the changes with sysctl
-a -p /etc/sysctl.conf

You can also tweak SO_SNDBUF in vlc via setsockopt


64-256k seems about right but the math is eluding me this morning.

You can turn off window scaling entirely, but that's not the right answer

 net.ipv4.tcp_default_win_scale = 0

the periodicity bothers me, it would be bad if that was synchronised,
to look at that problem would require some synchronous captures from
mutiple location.
On Sat, Apr 7, 2012 at 11:10
AM, Steinar H. Gunderson <sgunderson at bigfoot.com> wrote:
> On Sat, Apr 07, 2012 at 08:10:50PM +0300, Jonathan Morton wrote:
>> 12Mbps ADSL2+ in Finland (not at all far from Norway), via a standard
>> modem-router rather than my usual Linux system.  The LAN segment is
>> entirely wired full-duplex Ethernet.  The receiver is a Core i7 Windows PC
>> running the latest stable VLC, so it's not short of ability to play what it
>> receives.
>> And it's dropping more frames than it's playing.
> Have you tried the one at cesur.tg12? It's pacing things out a bit more.
> /* Steinar */
> --
> Homepage: http://www.sesse.net/

Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608

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