Steve’s Blog

Xen, CPUFreq and the Core i5 CPU

A while ago I updated my main fileserver (which was an old P4!) to a new Intel Core i5 CPU & associated hardware. I’ve managed to do some more tweaking today and found some very interesting things.

All Intel i5 CPUs (and probably the i3 & i7 as well) have this feature called Intel Turbo Boost. In short, what this does is to make your CPU run faster when it needs to – and as long as it doesn’t get too hot etc. This gives a nice performance boost without having to overclock the CPU all the time to squeeze out a little more performance.

There are however a few things you need to configure correctly to make sure Turbo Boost works on your system:

1) Configure cpuspeed to use the acpi_cpufreq module. Once this is done, have a look at scaling_available_frequencies. You should see something like this:

# cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_available_frequencies
3326000 3325000 3192000 3059000 2926000 2793000 2660000 2527000 2394000 1197000

This tells us we can scale between 1197Mhz and 3325Mhz. Note the entry for 3326Mhz. This is the way linux shows us the Intel Turbo Boost functionality.

2) It’s probably wise to use the ondemand governer for cpufreq. This will allow the system to ramp up its clock speed as required, then back it off automatically when things are a bit quieter.

3) Check to see that loads in Xen DomUs are correctly ramping up the CPU speed. To do this, I used this command:

watch “xm list; echo; cat /proc/cpuinfo | grep MHz”

This will show what DomU systems are running every 2 seconds, as well as the frequency that each core is running at. My system is currently an i5 661 (2 cores, 4 threads), so I see:

cpu MHz : 1197.000
cpu MHz : 1197.000
cpu MHz : 3325.082
cpu MHz : 3325.082

The last 2 entries are the hyperthreads for core0 and core1 respectively. You will note that the frequency of the extra threads do not change – but the cores will. When you do some activity in a DomU, you should see one or both of the cores clock up as required.

I love technology when it works properly

This Is True, Really!

It’s over 10 years since This Is True, Really! (TITR) was around on an Internet Radio site called NetRadio. It was well worth it – and I still get a good chuckle when I happen to come across some old shows on my network. Sadly, I could find no trace of TITR or what happens to Scot Combs and Tony Vircenis – A long lost jockey is out there but all I can remember is that technically how you write his name is “You can’t get potatoe salad a la carte”.

So, for your listening pleasure – Click on to re-live some past glory
Continue reading ‘This Is True, Really!’

Australian DAPs updated to 03-Jun-10

I’ve finally had time to sit down and update the DAPs collections. These are a compilation of every Airservices DAP plate grouped by airport. You can get the new DAPs here.

Xen disk IO on linux RAID5 array.

I’ve been playing with Xen for quite a while – having everything virtual is a godsend – however when you hit performance problems it can be a nightmare. After recently following some guides on Xen DomU installation I noticed that performance in the Disk IO area was just horrible – so I did what anyone in my shoes would do and wrote a quick guide that will squeeze MUCH more performance out of your Xen installations than following many of the existing (and outdated) guides.

This method works so well because it keeps all blocks aligned on your RAID5 array. If you do things differently, then you will get multiple writes as parity is updated on your array causing a huge penalty to performance.

Head over to the Xen Performance Guide

Using TSM with USB hard drives.

I’ve written up a quick page on how to use USB drives as removable storage on TSM.

Feel free to leave a comment on that page if you have any questions.