Questions[central-processing-unit](server)

I have a dual Opteron server running Linux with libvirt to host several VMs. The VMs work fine and the server processes OK, but I notice one CPU always runs about 69C (throttles at 70C) and the other runs about 15C.

This doesn't seem normal to me? Shouldn't they both be a little closer in temperature?

I'm not sure how to dianose any further. Maybe there isn't enough thermal paste on one of the CPUs?

Edit: The motherboard is ASUS KGPE-D16 and cooled by dual Noctua NH-U9DO fans.

Note that I think the temperatures might be degress above ambient, rather than absolute values? When the server is idling, the CPU temperatures drop to 2C and 13C. I am using the lmsensors configuration from here

I am trying to expose a hierarchy of home directories to a number of FreeBSD jails. The home directories are configured such that each is a unique ZFS dataset. The jails are used for development work and hence are created and destroyed on a regular basis.

My first thought was simply to use nullfs to mount /home inside the jail, but nullfs doesn't provide any way to access subordinate filesystems.

My second thought was to export the directories via NFS and then run the automounter daemon (amd) inside each jail. This would have Just Worked...if it were possible to perform NFS mounts inside a jail. But it's not.

My third thought was to run amd on the host and provision nullfs mounts into the jails...but amd support for nullfs doesn't exist.

My fourth thought was to go back to exporting the directories using NFS, because of course amd works with NFS, right? Unfortunately, rather than mounting a directory on the target mountpoint, amd likes to mount things in a temporary location (/.amd_mnt/...) and then create a symlink...which, of course, is useless inside the jail environment.

So maybe you could use nullfs to expose a subdirectory of /.amd_mnt to the jail? No! This brings us back to my first attempt, in which we find that there is no way to access subordinate filesystems using nullfs.

And then my head exploded.

Is there a good solution for what I'm trying to do? A bad solution would be to run a script after booting the jail that would create multiple nullfs mountpoints for each home directory, but this is pretty clunky -- it would need to be run periodically to take into account new directories or removed directories. So basically I would have to write a bad automounter.

There must be a better way. Help me, Serverfault, you're my only hope!

UPDATE 1: It occurred to me that I might be able to solve part of the problem with pam_mount, although this would at best be incomplete. Also, it's not clear from the documentation whether or not pam_mount can automatically create the target mountpoint. If it requires the mountpoint to exist a priori, this solution wouldn't be any better than the bad automounter I've already proposed.

UPDATE 2: As discussed in the answers below, setting VFCF_JAIL on the NFS filesystem does allow jails to perform NFS mounts. Unfortunately, the automounter continues to behave that are unhelpful, and when run in a jail appears to be very good at getting wedged in such a way that a system reboot is necessary to remove the process entry.

I know that certain processors are Big Endian and others are Little Endian. But is there a command, bash script, python script or series of commands that can be used at the command line to determine if a system is Big Endian or Little Endian? Something like:

if <some code> then
    echo Big Endian
else
    echo Little Endian
fi

Or is it more simple to just determine what processor the system is using and go with that to determine its Endianess?

I was doing some simple hand benchmarking on our (live) database server during non-peak hours, and I noticed that queries returned somewhat erratic benchmark results.

I had enabled the "Balanced" power saving plan on all our servers a while ago, because I figured they were nowhere near high utilization and this way we could save some energy.

I had assumed this would have no significant, measurable impact on performance. However, if CPU power saving features are impacting typical performance -- particularly on the shared database server -- then I am not sure it's worth it!

I was a little surprised that our web tier, even when at 35-40% load, is down-clocking from 2.8 Ghz @ 1.25V to 2.0 Ghz @ 1.15V.

I fully expect the down-clocking to save power, but that load level seems high enough to me that it should be kicking up to full clock speed.

Our 8-cpu database server has a ton of traffic, but extremely low CPU utilization (just due to the nature of our SQL queries -- lots of them, but really simple queries). It's usually sitting at 10% or less. So I expect it was downclocking even more than the above screenshot. Anyway, when I turned power management to "high performance" I saw my simple SQL query benchmark improve by about 20%, and become very consistent from run to run.

I guess I was thinking that power management on lightly loaded servers was win-win -- no performance loss, and significant power savings because the CPU is commonly the #1 or #2 consumer of power in most servers. That does not appear to be the case; you will give up some performance with CPU power management enabled, unless your server is always under so much load that the power management has effectively turned itself off. This result surprised me.

Does anyone have any other experience or recommendations to share on CPU power management for servers? Is it something you turn on or off on your servers? Have you measured much power are you saving? Have you benchmarked with it on and off?

Is there someway to record Task Managers info about CPU and memory usage to examine later? Or an equivalent tool?