Review your favorite Linux distribution.
Go Back > Forums > Linux Forums > Linux - Networking
User Name
Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.


  Search this Thread
Old 02-22-2011, 04:02 AM   #1
LQ Newbie
Registered: Feb 2011
Posts: 17

Rep: Reputation: 3
Question high network latency on lan, bridge, loopback...

Dear experts

I am puzzled with the following. I have installed Linux in two identical servers (AMD Opteron on ASUS MB, intel 82574 Lan-on-board, Scientific Linux 5.5 (RH rebuild)), configured them with KVM hypervisor, two bridges - one for eth0 physical, the other is libvirt default bridge with NAT function. iptables rules are only those defined by libvirt. SELinux is disabled. Network drivers are the latest from Intel.

I observe that my networking latency is subjectively high. Worth, it's different from one host to another. On one server ping to gives 0.052 ms, on the other .032 ms. Both values are rather high, since on another, Intel-based server in my organization I see observe 0.006 ms or less.

Ping from one server to the other on the same switch gives some 0.240ms and is not stable, i.e goes up and down by 0.030ms, while other servers give me .080ms is pretty stable

Also, pinging a guest VM from one host gives 0.250, on the other .500 ms - again factor n th2 and this totally ruins VM's network performance. Windows guests can only get 500Mbit host-to-guest throughput.

I wonder what can be the source of such high latency on the hosts? Any debugging tools experts couls suggests? Any tricks to improve latency? Could this be related to AMD CPU/chipset support? Something to do with linux bridge? What can cause almost 2-fold difference between hosts?

Here is my addition to sysctl.conf file on servers. Nothing helps.

net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.core.optmem_max = 524278
net.core.netdev_max_backlog = 250000

net.ipv4.tcp_rmem = 4096 262144  16777216
net.ipv4.tcp_wmem = 4096 262144  16777216
net.ipv4.tcp_timestamps = 0
net.ipv4.tcp_sack = 1
net.ipv4.tcp_low_latency = 0
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_moderate_rcvbuf = 1
net.ipv4.route.flush = 1
thanks a lot!


bridge, kvm, latency

Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ndiswrapper - high latency? the1sephiroth Linux - Wireless Networking 7 08-13-2008 06:58 AM
ssh over high latency connections amadkow Linux - Networking 9 10-12-2007 06:37 AM
64 latency for PCI bridge on an Abit BH6? stodge Linux - Hardware 6 08-10-2004 09:13 PM
Cannot create Network Bridge between LAN and WEB Hunza Linux - Networking 4 05-12-2004 01:58 AM
Sound latency too high stepse Linux - Hardware 0 09-23-2003 12:05 PM > Forums > Linux Forums > Linux - Networking

All times are GMT -5. The time now is 08:20 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration