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AMD vs Intel. Fight!
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2250
Location: Sydney

PostPosted: Thu Jan 14, 2021 7:19 am    Post subject: Reply with quote

Dan,

I bought a Ryzen 5900X last Dec-20 and it is much faster than my previous i7-8700K. Actually itís between 50% to 100% faster for my FE analysis, depending on the type of calculation.
I first got a 5900X + 64GB 3600MHz memory, but it kept crashing on multi-thread calcs. Changed to 3200MHz memory and it now doesn't crash. Presumably the quality of the silicon in the 3600MHz memory was a problem. I am not sure of the silicon quality of the 5900X !!

For my large array calcs using more threads, but only 2 memory channels is a significant bottleneck. I don't get much better performance above threads = cores, (which is similar with the 8700K)

I tried to find an easy problem to define and apply OpenMP! I have been doing testing of large matrix multiply using my developed code:
C[15000,12000] = A[15000,11000] x B[11000,12000] (see equation.com),
where partitioning is essential to reduce the memory<>cache bottleneck. (Vectors must be in cache for AVX to work efficiently and there are 3 levels of cache!) My main measure of performance is to calculate the number of floating point multiplies per second, as GFLOPS (10^9 flop/Sec). My coding approaches at partitioning produce 50 Gflop/s for i7-8700 and 100 Gflop/s for 5900X. These are significantly slower than MKL - DGEMM claimed performance (250+ Gflop/s for similar i5 processors), that I cannot approach (even allowing for MKL benchmarks count additions) (Equation.com report 22 Gflop/s for Opteron and 9.7 Gflop/s for Xeon which is slow)

Interesting that the Ryzen shows significant variability in gflops vs threads for my coding approaches, especially as threads exceeds cores. I7-8700 similarly stalls as threads exceed cores. This is an area I need to investigate further. My next processor will have more memory channels.
OpenMP with large arrays is not an easy coding problem. (large is array size >> cache size)
I will try to post some results when I can better describe the problem.
You can't just buy a different processor and use it. There is lots of tuning to do.
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DanRRight



Joined: 10 Mar 2008
Posts: 2237
Location: South Pole, Antarctica

PostPosted: Sun Jan 17, 2021 6:53 am    Post subject: Reply with quote

John,
So in summary you have got twice more cores inside Ryzen and 50 to 100% increase vs Intel ? Does this mean that the Ryzen single core performance is around the same as with Intel ?

Unfortunately i do not have anyone nearby with larger memory channel PCs. I have access to 10000 core Linux supercomputer which uses older Intel 12 core Xeon processors which would be not so interesting to test, and the code we use is written in C. Fortran version 19 with AVX should be there too but there is no one to ask how to use it, the good sysadmin left the team.

The only person i know by contacting him few years ago who has broad access to all world existing processors and who is also interested to test them is Ian Cutress from Anandtech. The UK guy by the way, former scientist, nice and easy going person, at least he was in the past before he started interviewing all the top CEOs in the IT industry. Try to convince him to run the test on 4, 6 and 8 memory channel computers. His own 3D particle moving code got huge benefits from AVX512. Plus he knew the former engineer at Intel who adjusted his code with AVX to get 3-4 even 5x increase in performance vs no-AVX. If he will find that some processors favor significantly cache size, memory channels or AVX with such important task as linear algebra i am sure there will be huge buzz in the industry. He touted his AVX speed increase with Intel processors vs AMD which do not have AVX512 last few years, and Intel clearly liked this. When we implemented in our codes AVX512 though the increase in performance was just 20% or less.
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JohnCampbell



Joined: 16 Feb 2006
Posts: 2250
Location: Sydney

PostPosted: Tue Jan 19, 2021 5:29 am    Post subject: Re: Reply with quote

DanRRight wrote:
Does this mean that the Ryzen single core performance is around the same as with Intel ?

I think that is too general a question. Ryzen is probably better, but I am comparing to Intel 8th gen.

I am finding Ryzen 5900X to be significantly faster than i7-8700K for the test cases I am considering. However there is considerable variability in the Ryzen performance.

My test cases involve large arrays/vectors; 100Mb to 3.5Gb. They appear to be too big to identify a benefit from 2x cache size (which I was hoping would be a plus)
At present (still in the learning phase), the variability in Ryzen performance appears to be due to a combination of variability in boost frequency and higher temperature with many threads. (high GFLOP matrix multiply is a compute intensive calculation) I have selected a Nocuta D15 air cooler, while a higher capacity water cooler might mitigate this. (I did not expect this to be as significnt a problem with 7nm silicon)

My other test case with an actual FEA calculation does show at least 50% improvement vs 8700, which is a plus for Ryzen.
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DanRRight



Joined: 10 Mar 2008
Posts: 2237
Location: South Pole, Antarctica

PostPosted: Tue Jan 19, 2021 8:20 am    Post subject: Reply with quote

Noctua is good air cooler, one of the best, but i still recommend to use reliable good company water cooler.
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