Network usage is overloading CPU
 

Hi,

recently my server become a little slow and lazy, so I started a small investigation what's going on and found out, that there is some problem with network.

All processes which uses network are able to use 99% of CPU time when they got any requests. First time i thought it's only a bad configured Apache but after some research I found even FTP or SSH does it if they have to do something more (for example getting data to another server using rsync).

So far I wasn't able to find a cause of this. No new software installed, only updated every few days. I have another server which have the same config, same software, same hardware and is updated in same days. But this one works without any problem. I think it's probably hardware (LAN) leaving me to it's creator. Is there some way how can I test if it's really LAN or just something bad happened to the system?

Also there is another issue - maximum speed dropped down to 20-30kB/s for both download or upload.

It's Debian Lenny 2.6.22-6 if you need to know :)

Thanks for any help

You can use tcpdump or wireshark to monitor the network packets. Hardware problems often show up as having many retransmitted packets, packets out of order, and that sort of thing.

Checkout, download/install/run iftop:
http://www.webhostingtalk.com/showthread.php?t=232209

...and stress junkie is right. If packets are arriving out of order to your server, each out of order packet causes a CPU interrupt. Get enough of those and there's your CPU usage.

Thanks. I'll try and will see :)

Heh, seems solved. I'll run some stress test but it works as it should now.

So, main cause of all this was stopped portmap, which every smart security book said "Turn it off for god sake!!" :) I just woke up and because of lack coffee in my veins, I just allowed it to start and reloaded server.

Thanks for help again and have a nice day ;)