[Simh] VAX emulation issues on Raspberry Pi

[Henry Bent]

On 31 July 2018 at 11:49, Timothe Litt <litt at ieee.org> wrote:

>
> On 31-Jul-18 10:08, Paul Koning wrote:
>
> On Jul 31, 2018, at 9:33 AM, Robert Armstrong <bob at jfcl.com> <bob at jfcl.com> wrote:
>
>
> FWIW, this may also say something about the quality of the code generation
> in gcc for ARM vs x86 processors, or it may even say something about the
> relative efficiency of those two architectures.
>
> One thing worth doing is to use the latest gcc.  Code generation keeps improving, and it's likely that architectures such as ARM see significant benefits in newer releases.
>
> 	
>
>
> Bob's SimH shows:
>
> Compiler: GCC 6.3.0 20170516
>
> The latest gcc is 8.1.0.
>
> It's a bit of a pain to build (I did it recently), but less so than in
> years past.
>
> On a Pi, it will take quite a while.  Be sure to use the latest
> dependencies - gmp, mpc, mpfr.  And put in some place like /usr/local - you
> don't want to replace the system compiler.
>
> Read http://gcc.gnu.org/wiki/InstallingGCC & https://gcc.gnu.org/install/
> index.html.
>
> I haven't played with isl - it may help, or it may expose new issues.
>
> You may be better off building a cross-compiler & building on a fast x86
> or other platform if you have one.  Besides computes, I/O on the PI can be
> pretty slow - USB is not a high-performance bus.  Especially if  you need a
> bunch of hubs.
>
> You also may need the latest binutils - if not for the build, for using
> the compiler.  Somewhere between the version I used previously and the new
> one, the object file format was enhanced incompatibly.
>
> ARM is a RISCish architecture, x86 is a very CISC one, burdened with a lot
> of backward compatibility.  Under the hood, it uses a lot of clever
> optimizations.  Both are moving targets, as are their compilers.  (GCC
> isn't the only choice.  Don't forget to try ICC if you want Intel's take on
> optimized code for their CPUs.  And Clang is coming along.)  Don't open the
> religious war over "relative efficiency"; the only thing that matters is
> whether code that you care about has performance that you deem adequate.
>
> Have fun.
>


I did a writeup a while back about various compilers and SIMH on x86, here
is the link from the archive:
http://mailman.trailing-edge.com/pipermail/simh/2015-December/014102.html

Profile-guided feedback is extremely helpful for SIMH.  If you are able to
recompile SIMH for your workload using feedback, the gains are extremely
significant.

-Henry
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