The Linux Kernel As An Exquisitely Sensitive Stability Test For Overclocked Systems

Running an overclocked PC is not a problem, provided that the PC is stable at the overclocked settings. Several programs are available to assess system stability by stress-testing the overclocked system. However, most overclockers do not know that the Linux kernel is an exquisitely sensitive tool to detect instabilities in an overclocked system. In fact, it is more accurate and sensitive than either Prime95 or IBT/LinX.

The Linux kernel supplies users with a dead simple method for measuring hardware instabilities - like those caused by an 'unstable' overclock. There is nothing special to install as this functionality seems to be naively included in the kernel itself. To use it, simply run a standard stress test such as Prime95 or Linpack and watch the output from dmesg. If the system is unstable due to insufficient voltage settings, excessive heat, it will report :

[Hardware Error]: Machine check events logged

I have seen the kernel throw these errors during a Prime95 run before Prime95 gave an error in the math. Furthermore, I have seen these errors appear even when Linpack did not detect that the settings are unstable, as evident by the residual number not chaining during the run when the error occurred.

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Using Linux

Probably the most newbie-friendly flavor of Linux is Ubuntu. Users can run it live off a CD or a USB without installing it to their systems. Further, it is pre-configured to boot into a GUI with network and hardware auto-detected. Download an image from Ubuntu - I recommend the 64-bit version as the 32-bit Linux suffers from the same <4 GB of memory limitation that the 32-bit Windows does.

Note : Don't feel like Ubuntu is your only option. There are many other Linux distributions out there from which to choose from.

Download the .iso file, burn it into a DVD drive, or copy it into a USB drive and boot off it. Ubuntu prompts users to either "Try Ubuntu" or "Install Ubuntu". Just hit the "Try Ubuntu" button and you will be dumped into the live Linux environment.

Here are a few suggestions for stress testing:

1. MPrime ---> Linux version of Prime95. Help to download and run MPrime.

2. LINPACK ---> backend to both LinX and IBT. Help to download and run LINPACK.

3. x264 video encoding.

4. Compiling something large like the Linux kernel.

I have seen on my own machine the ability to pass tests #1 and #2, but an inability to get more than 10 min into a x264 encode or to compile something 4-5 times without errors. It is important to test using several orthogonal stresses. While stressing, print the output of the kernel ring buffer. You can do this in one of two ways:

1. Open a terminal and type dmesg to see a snapshot.

2. Perhaps it would be more useful to be informed when something happens rather than typing dmesg over and over again! You can do this with the following command :

sudo cat /proc/kmsg

It may look like nothing is happening, but actually, the command more or less opened a connection to the ring buffer; it will update when something happens. To test it, plug in a USB flash drive. On my box, for example, it will report :

<5>[13393.025582] scsi 10:0:0:0: Direct-Access Kingston DataTraveler 112 1.00 PQ: 0 ANSI: 2
<5>[13393.026103] sd 10:0:0:0: [sdc] 7831552 512-byte logical blocks: (4.00 GB/3.73 GiB)
<5>[13393.026449] sd 10:0:0:0: [sdc] Write Protect is of<>133065]s 0000 sc oeSne 30 00

Anyway, what you really want to watch out for is this message :

[Hardware Error]: Machine check events logged

The kernel can throw these errors during an MPrime run before MPrime itself finishes the calculate and reports the error thus providing a very sensitive method to assess stability.

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CPU Stressing Programs

These are listed in two categories :

• High voltage demand
• Medium voltage demand

'High voltage' programs demand the most vcore when running, while 'Medium voltage' programs do not always call for the highest vcore when running, and as such, can be more prone to throwing errors for systems that are undervolted relative to the requested clock speed.

It is important to use at least one from each category to evaluate system stability. Ironically, machines can be more sensitive to selections from the 'medium voltage' category than from the 'high voltage' category.

Here's an example of an overclocked Intel Core i7-3770K CPU at 4.50 GHz, with the vcore at +0.020 V in offset mode, with all power saving features enabled.

Idle: 0.7440 V - 0.8320 V (varies).
Mprime small FFTs: 1.2880 V (steady).
Mprime large FFTs: 1.3040 V (steady).
Mprime blend: 1.2960 V (steady).
Linpack: 1.2320 V - 1.2720 V (varies).
x264 encoding: 1.2320 V - 1.2720 V (varies).
gcc compiling: 1.2720 V (steady).

This system can actually run with a vcore of +0.005 V (in offset mode) and remain stable in both MPrime and Linpack, but gets errors under both x264 and gcc. This is why I recommend selecting stress tests from both the 'higher voltage' category and the 'medium voltage' category.

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Memory Stressing Programs

Memtest86+ - Memtest86+ is a standard memory testing util and is packaged in Ubuntu and Knoppix.

Next Page - How To Stress Test The Overclocked System Using Linux

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