Raptor Lake AVX?

Chuck · 2023-03-13, 01:22

I have a new Core i9 13900K on which I am running double checks. I know this cpu does not support AVX-512. It does support AVX and AVX2 (see attached cpuid data). Prime95 (30.8b17) says it is "unknown Intel". It is using an FMA3 FFT instead of AVX.

I tried putting CpuSupportsAVX=1 and CpuSupportsAVX2=1 in local.txt, but it made no difference and the program still used an FMA3 FFT.

Is this something that might be addressed in the future?

sdbardwick · 2023-03-13, 01:58

What needs to be addressed?

Chuck · 2023-03-13, 02:12

That it is not using AVX.

sdbardwick · 2023-03-13, 02:27

Current order of performance:
AVX-512>FMA3>AVX>SSE x>legacy instructions (x87, MMX 3dNOW! ?)

There might be some sub-steps as well; IIRC there is a K9 (AMD) implementation wedged in there somewhere

Chuck · 2023-03-13, 02:30

Thanks, my bad. I thought AVX was faster. Prime95 still says "unknown Intel".

sdbardwick · 2023-03-13, 02:36

I think P95 gets the CPU name/flags/etc. from HWLOC, so updating that library might resolve the naming issue.

Prime95 · 2023-03-13, 02:44

Unknown Intel is harmless. The info is derived from family code returned by CPUID. New architectures need there family code added to prime95 source code.

Andrew Usher · 2023-03-13, 03:06

In other words, FMA3 is what you and most people call AVX2. I believe that CPUID (or whatever) will properly report the type of AVX supported even if the CPU isn't explicitly recognised, and Prime95 should use the best FFT as it is doing here.

henryzz · 2023-03-13, 12:59

Quote:

Originally Posted by Andrew Usher

In other words, FMA3 is what you and most people call AVX2. I believe that CPUID (or whatever) will properly report the type of AVX supported even if the CPU isn't explicitly recognised, and Prime95 should use the best FFT as it is doing here.

Strictly speaking they are different instruction sets although intel introduced them at the same time. I believe AMD supported FMA before AVX2(and the failed FMA4 before that). It wouldn't surprise me if only FMA+AVX2 code was added at the time as AMD performance at that time was terrible.

Mark Rose · 2023-03-13, 14:35

Quote:

Originally Posted by henryzz

Strictly speaking they are different instruction sets although intel introduced them at the same time. I believe AMD supported FMA before AVX2(and the failed FMA4 before that). It wouldn't surprise me if only FMA+AVX2 code was added at the time as AMD performance at that time was terrible.

AMD Piledriver and Steamroller supported FMA3 but not AVX2.

2023-03-13, 01:22	#1
Chuck May 2011 Orange Park, FL 2⁵·29 Posts	Raptor Lake AVX? I have a new Core i9 13900K on which I am running double checks. I know this cpu does not support AVX-512. It does support AVX and AVX2 (see attached cpuid data). Prime95 (30.8b17) says it is "unknown Intel". It is using an FMA3 FFT instead of AVX. I tried putting CpuSupportsAVX=1 and CpuSupportsAVX2=1 in local.txt, but it made no difference and the program still used an FMA3 FFT. Is this something that might be addressed in the future? Attached Thumbnails

2023-03-13, 02:27	#4
sdbardwick Aug 2002 North San Diego Coun 821 Posts	Current order of performance: AVX-512>FMA3>AVX>SSE x>legacy instructions (x87, MMX 3dNOW! ?) There might be some sub-steps as well; IIRC there is a K9 (AMD) implementation wedged in there somewhere Last fiddled with by sdbardwick on 2023-03-13 at 02:53 Reason: K9 info

2023-03-13, 02:36	#6
sdbardwick Aug 2002 North San Diego Coun 821₁₀ Posts	I think P95 gets the CPU name/flags/etc. from HWLOC, so updating that library might resolve the naming issue. Last fiddled with by sdbardwick on 2023-03-13 at 02:40

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2023-03-13, 01:58	#2
sdbardwick Aug 2002 North San Diego Coun 821 Posts	What needs to be addressed?

2023-03-13, 02:12	#3
Chuck May 2011 Orange Park, FL 2⁵·29 Posts	That it is not using AVX.

2023-03-13, 02:30	#5
Chuck May 2011 Orange Park, FL 2⁵×29 Posts	Thanks, my bad. I thought AVX was faster. Prime95 still says "unknown Intel".

2023-03-13, 02:44	#7
Prime95 P90 years forever! Aug 2002 Yeehaw, FL 8279₁₀ Posts	Unknown Intel is harmless. The info is derived from family code returned by CPUID. New architectures need there family code added to prime95 source code.

2023-03-13, 03:06	#8
Andrew Usher Dec 2022 3·13² Posts	In other words, FMA3 is what you and most people call AVX2. I believe that CPUID (or whatever) will properly report the type of AVX supported even if the CPU isn't explicitly recognised, and Prime95 should use the best FFT as it is doing here.