Monday, January 18, 2016

Prime95 and the Intel Skylake freeze Bug

Subtitle: CPU Fan testing !

There has been some press about the latest Intel firmware bug in its Skylake processors.

Now what might not be commonplace knowledge is that some bugs are known tolerated and worked around.  In the trade this is called errata.   To quote from the Intel literature


Normally when additionally functionality or bug fixes are shipped with newer revisions of the chip the /stepping/ level is changed.  However, unfortunately this is not always the case. Example of Software Guard Extensions  SGX

I think this also goes by the name of Intel Product Change Notification

In this case Intel has alluded to a work around being possible without recall and by change to Motherboard firmware.

Testing on OSX
The program that uncovered the Skylake processor freeze was the Great Internet Mersenne Prime Search.

So Marcus and Agata thought, sure we will run it too.  Not that we use Skylake processors at home yet, but if nothing else research uncovered that this is a great CPU stress testing program ...

Downloaded here

Installed on OSX ...

 Run this as a once off

On startup the program figures out how many executable Logical Processors you have available   (i.e. not Cores) and so for our humble 2012 Mac mini this is 8.

 Initially we are running at about 14% load

And finally we get upto about 97% CPU loading,  with testing only 7 out of 8 maximum threads.   As a realist, I selected 7, since this Mac is performing important work, I don't want to crash it.  I noted that during the benchmark the Mac Mini fan went into overdrive, it sounded like it was about to take off / explode :-)

Meanwhile under Windows
 I loaded the Windows 64 bit version of the program up

Like a chicken I only tested 16 threads not my maximum.   Again, I don't want to overhead / explode my system.  It is over 5 years old now and creaking :-(

Start the test

Our Xeon is pretty ancient by modern standards but hey it does the job right?

Never seen the system so busy!   Fans are working fast, but not to the takeoff standard as per frantic Mac Mini

I'm not a total idiot and so some CPU's are left idle during the torture test.

Overall I encourage you to download and run the Prime 95, Prime Number search software program.   It's a great stress test program and in the case of a Skylake CPU it could actually cause a processor freeze which would be good to know about.  

Motherboard manufacturers are apparently coming up with work arounds.  I don't really understand how.  Here is MSI's published response.

Great Internet Mersenne Prime Search
Intel Extreme Tuning Utility