Running Erlang on Xeon Phi

Question

How can I compile the VM and run Erlang programs on the Intel Xeon Phi coprocessor?

Answer 1

Intel Xeon Phi is not a typical x86_64 architecture, therefore it's not possible to run the official Erlang VM on it. The only way to do it is to use cross-compilation and build the VM yourself on a different (host) machine where Erlang is supported, so that it runs on a target system (Phi in this case).

Xeon Phi also supports slightly different instruction set than a typical x86_64 architecture, so you also need to edit the code. If you just cross-compile the VM without touching the code, you will probably get an error:

/tmp/iccvaLP3vas_.s: Assembler messages:
/tmp/iccvaLP3vas_.s:25794: Error: `mfence' is not supported on `k1om'

So first of all you need to add #ifndef clauses around memory fence instructions, which are not supported on Phi (mfence, lfence and sfence). This boils down to opening the erts/include/internal/i386/ethr_membar.h file and adding following preprocessor directives:

#ifndef __MIC__
...
#endif

around __asm__ statements in funtions ethr_mfence__, ethr_sfence__ and ethr_lfence__ e.g.

static __inline__ void
ethr_mfence__(void)
{
#if ETHR_SIZEOF_PTR == 4
    if (ETHR_X86_RUNTIME_CONF_HAVE_NO_SSE2__)
        ETHR_NO_SSE2_MEMORY_BARRIER__;
    else
#endif
#ifndef __MIC__
    __asm__ __volatile__ ("mfence\n\t" : : : "memory");
#endif
}

Now you can try to cross-compile it. First download the sources (in my case Erlang VM 17.5), then run:

$ cd otp_src_17.5
$ export ERL_TOP=`pwd`;
$ ./configure \
    --host=k1om-unknown-linux-gnu \
    --build=x86_64-pc-linux-gnu \
    --without-termcap \
    --without-javac \
    --without-ssl \
    --prefix=/path/to/my/new_installation \
    CC=icc \
    CFLAGS=-mmic \
    LDFLAGS=-mmic \
    DED_LD=icc \
    DED_LDFLAGS="-mmic -shared -Wl,-Bsymbolic" \
    DED_LD_FLAG_RUNTIME_LIBRARY_PATH="-Wl,-R"
$ make
$ make install

icc is the official Intel Compiler and -mmic flag is required for compiling for Xeon Phi. The host and build flags are the systems/architectures of respectively the machine where you compile and the machine which you compile for (Phi). In my case they had following values, but if it's different for you, you might want to use the config.guess script which automatically detects your OS/CPU architecture.

$ ./config.guess
$ x86_64-pc-linux-gnu

And that's it! Now you should be able to ssh on your Phi and run Erlang.

$ ssh my-phi-coprocessor
$ cd /path/to/my/new_installation/
$ export PATH=`pwd`/bin:$PATH;
$ erl -version
Erlang (SMP,ASYNC_THREADS) (BEAM) emulator version 6.4