[mythtv-users] HDHomeRun Hint: Ethernet buffer size

Jon Boehm boehm100 at comcast.net
Tue Sep 4 19:22:15 UTC 2007


Hi,

I was getting horrible pixelation, missing time, dropped channel locks, 
and strange slow motion artifacts from some of my 1080i channels.  I'm 
pretty sure I have fixed the problem now.  I turns out my Ethernet 
buffers were overflowing.  I have a F/B machine with 4 tuners total. 
When recording and commercial scanning the machine maxes out.

The silicon dust how-to mentions this:
Packet loss 

On slower machines or machines under high load the maximum receive 
socket buffer size for the system should be increased to 1MB:

sysctl -w net.core.rmem_max=1048576

-----------

While this is all that may be required I did some searching and ended up 
doing this since I have plenty of RAM:

This is my sysctl.conf file

#increase TCP maximum buffer size
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216

# increase linux autotuning TCP buffer limits
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

# don't cache ssthresh from previous connection
net.ipv4.tcp_no_metrics_save = 1
# recommended to increase this for 1000 BT or higher
net.core.netdev_max_backlog = 2500

Once you change these run the command

sudo sysctl -p

A link about this.

http://dsd.lbl.gov/TCP-tuning/linux.html

A couple others I use

net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack =1
net.ipv4.tcp_window_scaling = 1

Another link

http://www.speedguide.net/read_articles.php?id=121




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