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Old 2017-04-25, 21:03   #1
Apr 2017

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Default How much is it about FLOPS


I have started mprime on an old i5 2500K, and it is so slow.
I am eager to setup a work station, to learn about micro architectures and GIMPS in general.

I have been looking at ryzen, but as this post states the zen architecture performance is half that of intel core's for double precision. 16vs8 IPC.
Can Ryzen perform better on other tasks than Lucas-Lehmer? (this question is revealing I am trying to get knowledge in this thread rather than reading thoroughly the documentation, apologies...)
Do you know if there would be architecture changes in later revision Zen2?

How much does LL rely on 64bits FLOPS? How much is it about the rest of the micro architecture : cores, ram size or speed, cache, else? From what I have read so far, GIMPS is optimized pretty much only for Intel. What about archis like Risc V, POWER PC or others?

What about GPU computing? About power efficiency and GIMPS support (AMD VEGA in mind), I found it hard getting an overview.

Last fiddled with by maxzor on 2017-04-25 at 21:07
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Old 2017-04-25, 22:00   #2
Mark Rose
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Jan 2013

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If you *only* do gaming or GIMPS, then Intel may be right for you.

If you're doing lots of compiling, multitasking, etc., you'll likely benefit from the extra cores/threads of Ryzen.

The Zen core architecture runs FMA and AVX2 at hourly half the speed of Intel per clock. The most optimized Prime95/mprime code uses FMA and AVX2, so this greatly impacts Zen's performance.

It's unlikely that the next Zen iterations will switch to faster FMA and AVX2. AMD determined that most code doesn't use these instructions and that it would give a greater advantage in most cases to include more cores and cache.

The best part about Zen is that the next series of Intel chips is supposed to ship with more cores, so we'll still end up getting more for our dollars for GIMPS.

Right now the sweet spot is probably an i5-7500 with DDR4-2400, dual channel with dual rank DIMMS.

For GPU computing the sweet spot is probably the GTX 1080 Ti, considering you also have to buy host hardware for each card. I have a GTX 1070 and a 1060 and the 1070 is a much better value when it comes to performance/power consumption. In general, one down from the top of a graphics line is usually the best value for computation, e.g. GTX 1070, RX 470, etc.

Vega should be out in the next two months and I'm sure someone will buy a Vega card and benchmark it.
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Old 2017-04-25, 23:25   #3
VBCurtis's Avatar
Feb 2005
Riverside, CA

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Prime95 takes such strong advantage of FMA/AVX2 that it runs out of memory bandwidth on most quad-core chips. That's why the first reply specified memory speed and dual-rank; those specs minimize the memory bottleneck that P95 suffers within a reasonable budget.

There are faster memory kits available, but they generally come at the cost of looser timings, which then causes P95 to wait on memory bus a bit; the overall gist of benchmarks posted 'round these parts is diminishing returns on fasterMhz-but-slower-timings memory sticks.

Future memory sticks with higher Mhz ratings with the tighter timings available at 2400mhz may improve P95 performance.

Folks with prebuilt machines that have slower memory sticks (say, 1600) often find that 3 cores of P95 produces as much (nearly, say within 6-8%) as 4 cores, because 3 cores already fully uses all available memory bandwidth; this is convenient for windows and background processes, which can then have a core unto themselves.

You should peruse the Ryzen threads around here for empirical data on how Ryzen's memory bus keeps up with CPU demands on P95.
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Old 2017-04-27, 21:08   #4
VictordeHolland's Avatar
"Victor de Hollander"
Aug 2011
the Netherlands

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Originally Posted by maxzor View Post
I have started mprime on an old i5 2500K, and it is so slow.
I own a i5 2500k too (@4.0GHz), but I don't think it is slow. If you've ever tried Atom/Celeron/Pentium notebooks and PCs your definition of slow changes .
Yeah, there are newer (faster) architectures, but for most things it is still fast enough. For Prime95 the i5 2500k is as fast as a Ryzen (optimizations might change that balance in the future).
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