[Lxc-users] Help troubleshooting declining performance / high %SI CPU when running 9 Ubuntu 10.04 LXCs

[Iliyan Stoyanov]

Hi Ivan,

you should probably do a monitoring with iostat and vmstat also. On the
top of my head I can think of at least 3 or 4 reasons why this might be
happening. I have similar problems with a simple laptop machine without
LXC containers on it (and don't have such on a server with a bunch of
containers on it). In my experience with bad SI everything always come
back to be RAM related. Also check your filesystem performance. Most of
the FSes nowadays keep a ton of the journalling info in RAM. I know my
response is not exactly an answer to your specific question but I hope
it might give you some pointers for better monitoring of the situation.

BR,

--ilf

On Thu, 2011-09-15 at 09:12 -0600, Ivan Fetch wrote:

> Hello,
> 
> I've inherited a Sun 4540 (thumper) machine running 9 LXC containers. During the past few weeks we've been troubleshooting a decline in performance, which ends up in high %SI (software interrupt) CPU usage. I'm hoping someone here can help troubleshoot and narrow down what the real issue is - this one really has me stumped.
> 
> THis box has 48 disks, 5 RAID6 which are in a RAID0, using md. Two NICs are bonded together, and a bridge is used for the box's IP, and the LXC network interfaces.
> 
> Linux is Ubuntu 10.04, LXC 0.6.3 , containers are also 10.04. Containers run Apache, some custom image processing, gaussian, and FTP server...
> 
> The box performs well after a reboot, with all containers back online. After ~5 days, we notice that the box is sluggish, and backup jobs (Netbackup) get less than 1Mb/sec over the network. CPU eventually reaches 61% SI. OTher processes (I am looking at ps -ax -o pcpu ..... |sort -n) begin taking much higher percent CPU than they should need, I imagine because the high %SI is taking cycles; E.G. I'll briefly see ps or sort or a shell using 6% CPU. Top shows %sy between 5-20, %wa under 5.
> Memory (32Gb) is mostly used for cache, and there is no swapping.
> 
> I know next-to-nothing about tracking down the cause for high %SI CPU usage.
> 
> 
> Thanks for any help looking at this with a clear head,
> 
> - Ivan
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