Prime95 26.6 How To Get The
Prime95 26.6 Software Was Unheard
Prime95 26.6 Code Paths Causing

By generating a power consumptionFFT size profile as above, specific points and ranges can be picked out: It should be noted that the Cache and CPU Core test ranges should generally only be run with FMA3 and AVX disabled, unless youre specifically aware youll be running workloads that stressful.

Press question mark to learn the rest of the keyboard shortcuts Log In Sign Up User account menu 235 PSA: Dont Use Prime95 Until Youve Read This.

The Much-Requested Short Version: None of the presets do what they say they do - exactly what they really do depends on how much cache your CPU has per thread.

If you turn off AVX and FMA3, you arent testing instructions that are being increasingly used in more and more every day applications and games.

Blend test is super-sketchy as its load varies a LOT depending on whether you have hyperthreadingSMT or not.

Hey, I said it would be short, I didnt say it wouldnt still be confusing;) Background Prime95 is a distributed computing effort searching for Mersenne prime numbers.

Version 1 was released in 1996 and there have been a huge number of improvements, bug fixes and optimizations for specific CPUs and instruction sets since then.

The torture test feature is intended to allow those contributing to the project to ensure their CPUs are stable under the heavy loads its routines generate and has been considered the platinum standard in the overclocking community for a long time.

Prime95 26.6 Software Was Unheard

The introduction of support for AVX instructions caused controversy among overclockers with the greatly increased power consumption and temperatures generated by testing using an instruction set whose use in other software was unheard of leading many to label Prime95 unrealistic and abandon it for other stress testing regimes.

With support today for AVX and FMA3 available in specialised FFT routines and adoption of those instruction sets in every day software and games on the rise, its time to reconsider stability testing regimes for these instruction sets.

Torture Test Parameters Prime95s torture test dialog includes options to configure custom stress tests alongside its three built-in presets.

Prime95 26.6 How To Get The

Understanding how the options change the behavior of the FFT routine that the stress test uses is an important part of learning how to get the best out of Prime95.

The most important option is the Run FFTs in-place check box.

With this enabled the FFT routine will use the smallest memory footprint possible, while unchecking this box allows you to enter a figure in the Memory to use box, setting a custom memory pool that the routine will spread its data out into.

The next option to understand is the FFT test range, configured through the Min and Max FFT size boxes.

With Run-In-Place mode enabled, the amount of memory the FFT routine needs is directly connected to the FFT size: Varying the data set size required to run FFT routines in Run-In-Place mode is the main method of customizing which parts of your system are being placed under heavy stress by changing where in the cachememory hierarchy the CPU core bottleneck lies: The data sets required for smaller FFTs fit entirely inside the CPU cache, allowing the cores to run at their fastest possible rate.

As the data sets increase in size and overflow from the cache into system RAM, power consumption drops off smoothly as the frequency of cache misses increases and the CPU cores begin to become bottlenecked, levelling off once the data set becomes too big for cache to be of any practical use and the cores are entirely at the mercy of system memory performance.

While this is easily seen in the above chart for the FMA3 and AVX routines, it is less obvious that the SSE routines also follow the same load pattern for the cache and memory.

The primary difference is that the performance of the SSE routine doesnt scale anywhere near as well as the AVX or FMA3 routines when the memory bottleneck is removed.

Prime95 26.6 Code Paths Causing

NB: Power consumption measurements do not provide a basis for performance comparison across routines due to differences in the code paths causing variations in the efficiency of each routine) Given that the performance profiles of the various FFT sizes is based on resource contention, we now have to consider another factor that makes running Prime95 a lot trickier than you might be thinking so far - CPUs come with different thread counts and cache quantities.

Lets turn HyperThreading off on our 4770K and see what effect that has on the power consumption profile: Without HyperThreading enabled the power consumption in most cases drops by the expected approx.

L3 cache space, it takes a much larger FFT size for the CPU to begin seeing cache-misses.

Effectively, this makes the In-Place Large FFTs test operate inconsistently across CPUs with different ratios between their L3 cache size and thread count.

This makes the concept of universal preset FFT ranges for specific tests obsolete.

Going back to the idea of specific FFT sizes and ranges being suited to testing certain system components, it may be possible to generate sets of tests based on the cachethread ratio applicable across all CPUs that share that metric.

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