CentOS 6.7 : ethtool “rx_discards” errors

Here is a memo about “rx_discards” error.

Reference

http://wiki.centos.org/Events/Dojo/Bangalore2014

(Topic: Network Debugging -> Slides: Network-jkalliyat.pdf )

# cat /etc/centos-release CentOS release 6.7 (Final) # uname -ri 2.6.32-573.3.1.el6.x86_64 x86_64

I found a number of “rx_discards” is counting up on one of interfaces, which processes approximately 300,000 UDP packet / sec.

In my case, I was able to solve that by increasing buffers on that interface.

rx_discards errors on interface ‘eth0’

# while :; do ethtool -S eth0 | grep discard ; sleep 1; done      tx_discards: 0     rx_discards: 49070     tx_discards: 0     rx_discards: 49071

Red line: current setting

# ethtool -g eth0 Ring parameters for eth0: Pre-set maximums: RX:             2047 RX Mini:        0 RX Jumbo:       0 TX:             511 Current hardware settings: RX:             200 RX Mini:        0 RX Jumbo:       0 TX:             511

Increase RX buffers to 2047 from 200

# ethtool -G eth0 rx 2047

After increasing buffers.

# ethtool -g eth0 Ring parameters for eth0: Pre-set maximums: RX:             2047 RX Mini:        0 RX Jumbo:       0 TX:             511 Current hardware settings: RX:             2047 RX Mini:        0 RX Jumbo:       0 TX:             511

Here are my kernel parameters.

sysctl -w net.ipv4.tcp_rmem="4096 873800 4194304" sysctl -w net.ipv4.tcp_wmem="4096 873800 4194304" sysctl -w net.ipv4.tcp_mem="5194304 5194304 5194304" sysctl -w net.core.rmem_default=4194304 sysctl -w net.core.wmem_default=4194304 sysctl -w net.core.rmem_max=4194304 sysctl -w net.core.wmem_max=4194304 sysctl -w net.core.optmem_max=20480 /sbin/ethtool -G eth0 rx 2047