# Stress Test

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## Introduction

Running an overclocked PC is totally fine provided that the PC is stable at the overclock settings. There are several programs available to assess system stability through stress testing the system and thereby the overclock level. The steps of overclocking a PC are beyond the scope of this article, but there is pretty inclusive guide written by graysky on the topic: Overclocking guide.

Note: The linked guide is a bit dated. More contemporary guides are recommended for modern hardware.

## Discovering Errors

Some stressing applications like mprime and linpack (see below) have built in consistency checks to discover errors due to non-matching results. A more general and simple method for measuring hardware instabilities can be found in the kernel itself. To use it, simply watch the output from the kernel ring buffer by this command:

    # cat /proc/kmsg

The key error to watch for looks like this:

    [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.

## CPU Stressing Programs

These are listed in two categories: 'higher demand voltage' and 'medium demand voltage'. It is important to use some from each category to evaluate system stability. Ironically, machines can be more sensitive to selections from the 'medium demand' category than from the 'high demand' category. 'Higher demand voltage' programs demand the most vcore when run due to intense hardware usage. 'Medium demand 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 clock speed requested.

Example on an overclocked i7-3770K (4.50 GHz); vcore is +0.020 V in offset mode with all powersaving 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 machine running with a vcore of +0.005 (in offset mode) remains stable in both mprime and linpack for hours, but throws errors under both x264 and gcc after only several minutes.

Voltage Demand | Program | Description
--- | --- | ---
Medium
Cc/Gcc | Both cc/gcc compilation is a great method of stress testing. Both are available in the base-devel group.
HandBrake-cli | handbrake-cli can be used to encode using high quality settings.
Systester | systesterAUR Systester is a multithreaded piece of software capable of deriving values of pi out to 128,000,000 decimal places. It has built in check for system stability.
High | mprime | mprime-binAUR factors large numbers and is an excellent way to stress CPU and memory.
linpack | linpackAUR - Linpack makes use of the BLAS (Basic Linear Algebra Subprograms) libraries for performing basic vector and matrix operations. and is an excellent way to stress CPUs for stability.

## Stressing CPU and Memory

### Mprime (Prime95 for Windows and MacOS)

Prime95 is recognized universally as one defacto measure of system stability. Mprime under torture test mode will perform a series of very CPU intensive calculations and compare the values it gets to known good values.

Prime95 for Linux is called mprimeAUR and is available in the AUR.

Warning: Before proceeding, it is HIGHLY recommended that users have some means to monitor the CPU temperature. Packages such as Lm_sensors can do this.

To run mprime, simply open a shell and type "mprime"

    $ mprime

Note: If using a cpu-frequency scaler such as cpufrequtils or powernowd sometimes, users need to manually set the processor to run with its highest multiplier because mprime uses a nice value that doesn't always trip the step-up in multiplier.

When the software loads, simply answer 'N' to the first question to begin the torture testing:

    Main Menu

    1.  Test/Primenet
    2.  Test/Worker threads
    3.  Test/Status
    4.  Test/Continue
    5.  Test/Exit
    6.  Advanced/Test
    7.  Advanced/Time
    8.  Advanced/P-1
    9.  Advanced/ECM
    10.  Advanced/Manual Communication
    11.  Advanced/Unreserve Exponent
    12.  Advanced/Quit Gimps
    13.  Options/CPU
    14.  Options/Preferences
    15.  Options/Torture Test
    16.  Options/Benchmark
    17.  Help/About
    18.  Help/About PrimeNet Server

There are several options for the torture test (menu option 15).

- Small FFTs (option 1) to stress the CPU
- In-place large FFTs (option 2) to test the CPU and memory controller
- Blend (option 3) is the default and constitutes a hybrid mode which stresses the CPU and RAM.

Errors will be reported should they occur both to stdout and to `~/results.txt` for review later. Many do not consider a system as 'stable' unless it can run the Large FFTs for a 24 hour period.

Example `~/results.txt`; note that the two runs from 26-June indicate a hardware failure. In this case, due to insufficient vcore to the CPU:

    [Sun Jun 26 20:10:35 2011]
    FATAL ERROR: Rounding was 0.5, expected less than 0.4
    Hardware failure detected, consult stress.txt file.
    FATAL ERROR: Rounding was 0.5, expected less than 0.4
    Hardware failure detected, consult stress.txt file.
    [Sat Aug 20 10:50:45 2011]
    Self-test 480K passed!
    Self-test 480K passed!
    [Sat Aug 20 11:06:02 2011]
    Self-test 128K passed!
    Self-test 128K passed!
    [Sat Aug 20 11:22:10 2011]
    Self-test 560K passed!
    Self-test 560K passed!
    ...

Note: Users suspecting bad memory or memory controllers should try the blend test first as the small FFT test uses very little memory.

### Linpack

linpackAUR makes use of the BLAS (Basic Linear Algebra Subprograms) libraries for performing basic vector and matrix operations. It is an excellent way to stress CPUs for stability (only Intel CPUs are supported). After installation, users should copy `/usr/share/linpack/linpack.conf` to `~/.config/linpack.conf` and adjust it according to the amount of memory on the system.

### Systester (AKA SuperPi for Windows)

SystesterAUR is available in the AUR in both cli and gui version. It tests system stability by calculating up to 128 millions of Pi digits and includes error checking. Note that one can select from two different calculation algorithms: Quadratic Convergence of Borwein and Gauss-Legendre. The latter being the same method that the popular SuperPi for Windows uses.

A cli example using 8 threads is given:

    $ systester-cli -gausslg 64M -threads 8

### Intel Processor Diagnostic Tool

Note: This section only applies to Intel CPUs.

The Intel Processor Diagnostic Tool is a tool that verifies the functionality of an Intel Microprocessor by stress testing the CPU. A Fedora Linux LiveUSB ISO images are available. The LiveUSB image allows you to stress test your machine without using your main operating system; such method might be useful in extreme cases especially when dealing with cold reboots/crashes.

Burn the image to a USB stick by using dd or Gnome Disks and then boot the Live CD. Once booted, open the terminal and type the following command to install Intel Processor Diagnostic Tool for 64-bit machines:

    $ install64

Once it is installed, you can run the Diagnostic Tool by clicking on the IPDT Icon that is located on the desktop.

## Stressing Memory

A very good program for stress testing memory is Memtest86+. It is based on the well-known original memtest86 written by Chris Brady. Memtest86+ is, like the original, released under the terms of the GNU General Public License (GPL).

### Running Memtest86+

Either download and burn the ISO to a CD and boot from it, or install memtest86+ from [extra] and update GRUB which will auto-detect the package and allow users to boot directly to it.

Tip: Allowing Memtest86+ to run for >10 cycles without errors is usually sufficient.
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