Error with avx2 when compiling for Intel Haswell architecture about blasfeo HOT 17 CLOSED

what is your complier?

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gcc (GCC) 4.4.7 20120313 (Red Hat 4.4.7-4)

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Apparently you need at least gcc 4.7 for that.

You can try to replace -mavx2 with -mavx here
https://github.com/giaf/blasfeo/blob/master/Makefile.rule#L121
(and possibly remove -mfma if it complains about), and see if you can still use the assembly kernels optimized for Haswell.

Otherwise, either you use a more recent compiler, or a older target (losing some performance).

Let me know how it goes :)

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Thank you, sorry for my ignorance :/ - I'd rather update gcc. Updates soon

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Looks like I need a newer Red Hat distribution to use gcc 4.8; While I'm downloading the newer version, I tried replacing -mavx2 to -mavx and it didn't work. Also, tried removing -mfma and same error (assembler errors, it seems). Curiously, if I use INTEL_CORE it works. Could it be an error in architecture selection?

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By Intel Core architecture (not the Core brand name for Core i7, i5, ...), I mean this
https://en.wikipedia.org/wiki/Intel_Core_(microarchitecture)
that is a rather old architecture.
In BLASFEO, the code for this target uses instructions up to SSE4
https://en.wikipedia.org/wiki/SSE4
that in double precision can perform 1 multiplication and 1 addition of 2-wide vectors per clock cycle.

Intel Sandy Bridges introduces the AVX instruction set
https://en.wikipedia.org/wiki/Advanced_Vector_Extensions
that in double precision can perform 1 multiplication and 1 addition of 4-wide vectors per clock cycle.

Intel Haswell introduces the AVX2 and FMA3 instruction sets
https://en.wikipedia.org/wiki/Multiply%E2%80%93accumulate_operation#Fused_multiply.E2.80.93add
that in double precision can perform 2 fused-multuply-add of 4-wide vectors per clock cycle.

Each new computer architecture supports the old instructions, plus possibly additions.
So, using an older target (as e.g. Core or Sandy Bridge) works for you, but you are not fully exploiting the new instruction sets.

Old compilers are not aware of recent instruction sets, so even if you have an Haswell processor, the gcc 4.4.7 compiler can not generate code with AVX2 and FMA instructions.

In any case, even with an old linux distro you can always install more recent versions of gcc from source.

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Thank you. Yeah, so in my case it is Haswell indeed.

I'm a very poor Linux user, so I keep trying to figure things out from forums. I'll give it one more try on installing newer versions from source as you suggested. Sorry to keep giving you trouble.

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No problem, I'm glad to help.

Otherwise you can simply use the Sandy Bridge target, it's not the best one, but the speed up using the Haswell target is always less than 2x.

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Sandy Bridge works fine too. I'll work on the newer gcc and report back if I'm successful with Haswell then.

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GCC updated to 4.8 and BLASFEO now compiles with Haswell target!

Thank you so much!

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@giaf , I think the ISA tests aren't good enough.
They only check if the processor is capable of the ISA (Which you could do with cpu_id()).
You should also check if the correct headers are set.
So at least add an ISA command like: _mm256_loadu_pd or _mm_loadu_pd. It is better to selects commands for AVX2 as well (Something with integer).

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They only check if the processor is capable of the ISA (Which you could do with cpu_id())

This is provided as a runtime function blasfeo_processor_cpu_features the user of the library can call to see if the current processor supports the compiled version.

So at least add an ISA command like: _mm256_loadu_pd or _mm_loadu_pd.

The ISA tests directly compile the assembly mnemonics to test for support of the requested architecture, since the BLASFEO source uses assembly for the target-specific kernels instead of intrinsics. I don't think it uses any intrinsics in the code, so it shouldn't need to include special headers, but @giaf would know better than I about that.

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That's not the case.
For instance, try to compile the project on Skylake without the flag -mavx2. You will get an error.

The current CMAKELists.txt adds the flags but it is better the tests will test the correct flags are indeed added and effective.

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Hmm, there are some AVX intrinsics in the code apparently. I had thought everything was done in pure assembly. It should be easy for me to add those to the ISA tests though.

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Yes some easy stuff like BLAS 1 routines is vectorized with intrinsics instead of pure assembly.

@imciner2 great if you can do that!
BTW your ISA tests turned out to be a great feature to use BLASFEO in acados :)

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BTW I noticed that on some ARM architectures you still need to enable NEON with an assembler flag otherwise the assembler would complain. But in this case no headers are needed.

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great if you can do that!

Done in PR #122 for the X86 intrinsics (which are the only ones used in the code currently).

BTW your ISA tests turned out to be a great feature to use BLASFEO in acados :)

Great to hear. That was the main reason I developed them, since I remember seeing the issues just setting a high default caused for some people's computers when installing it.

BTW I noticed that on some ARM architectures you still need to enable NEON with an assembler flag otherwise the assembler would complain. But in this case no headers are needed.

Yea, some ARM architectures get really picky about the flags needed to compile unfortunately.

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