My personal benchmarks prove that applications written in D are 5% to 20% slower than identical code written in C and compiled with Intel C compilter 9. Does anyone know what to do with this problem? Is it a compiler specific problem (ie: D compiler lacking all the optimisation parameters) or the standard d libary or what??

Any information/idea would be appriciated. Before starting a big project, speed issues with D seems to be the biggest obstacle to overcome.

Teoman Soygul,
Alsoft.

Teoman Soygul wrote:
> My personal benchmarks prove that applications written in D are 5%
> to 20% slower than identical code written in C and compiled with
> Intel C compilter 9. Does anyone know what to do with this
> problem? Is it a compiler specific problem (ie: D compiler lacking
> all the optimisation parameters) or the standard d libary or
> what??
> 
> Any information/idea would be appriciated. Before starting a big
> project, speed issues with D seems to be the biggest obstacle to
> overcome.

If it's identical code, then it's a compiler optimization issue, as identical C code compiled with D should produce identical results. You can try using the D profiler to see if the slowdown is in any specific place.

5% to 20% are generally not big obstacles to overcome, as they are often in one or two spots that can be hand optimized (or written in assembler). It's also my experience that until it reaches 2:1, few people even notice it. Even the same program will vary 5 to 10% in execution time from run to run.

Teoman Soygul wrote:
> My personal benchmarks prove that applications written in D are 5%
> to 20% slower than identical code written in C and compiled with
> Intel C compilter 9. Does anyone know what to do with this
> problem? Is it a compiler specific problem (ie: D compiler lacking
> all the optimisation parameters) or the standard d libary or
> what??
> 
> Any information/idea would be appriciated. Before starting a big
> project, speed issues with D seems to be the biggest obstacle to
> overcome.
> 
> Teoman Soygul,
> Alsoft.

I think even Microsoft's compiler is 5-20% slower than the Intel's compiler, depending on the particular code in question (particularly SSE optimizeable things).  So I don't think this speed difference is something to be so worried about.

Still, there's a big difference between 5% and 20%.  Do you have any observations about what sorts of things put you in the 20% category?

--bb

Teoman Soygul wrote:
> My personal benchmarks prove that applications written in D are 5%
> to 20% slower than identical code written in C and compiled with
> Intel C compilter 9. Does anyone know what to do with this
> problem? Is it a compiler specific problem (ie: D compiler lacking
> all the optimisation parameters) or the standard d libary or
> what??
> 
> Any information/idea would be appriciated. Before starting a big
> project, speed issues with D seems to be the biggest obstacle to
> overcome.
> 
> Teoman Soygul,
> Alsoft.

One thing you might want to do is to also compare with C code compiled using the Digital Mars C compiler since dmd and dmc use the same back end.  This should help clarify what's due to inherent differences in the languages and what's just differences in compiler optimization.

--bb

"Do you have any observations about what shorts of things put you in the 20% category?"

- Luckly the code requiring sheer processing power like math
functions(trigs, logs...), b-tree creation, compression, D code
runs only 5-6% slower (an averaged mean) compared to Intel C
compiler.
- Unfortunately, processes requiring sheer memory access like
memcopy, mem alloc, de-alloc, stream copy is nearly almost 15->20%
slower at D. (note that, code is totally identical).

I'll post these results on my blog once I put them into a good graphed format so we can discuss it even further. with my limited knowledge on compilers, what i've seen is that intel c compiler has many ingenious optimisations. maybe there can be a way to put the same ideas into D compiler. (i hope)

Teoman Soygul wrote:
> My personal benchmarks prove that applications written in D are 5%
> to 20% slower than identical code written in C and compiled with
> Intel C compilter 9. Does anyone know what to do with this
> problem? Is it a compiler specific problem (ie: D compiler lacking
> all the optimisation parameters) or the standard d libary or
> what??

If you can, try to profile the code and see where the difference lies. How long does the application run, is the code identical, etc?  5% for a very short-running app could be attributed to the garbage collector initialization and termination, for example, but this wouldn't be a factor in longer running apps.


Sean

%u wrote:
> - Unfortunately, processes requiring sheer memory access like
> memcopy, mem alloc, de-alloc, stream copy is nearly almost 15->20%
> slower at D. (note that, code is totally identical).

Keep in mind that D's allocator includes a garbage collector. To really do an apples-to-apples comparison, your benchmarking code should create lots of temporary objects. In D, the GC will handle all allocations and de-allocations. In C++, your objects will have to be manually created and destroyed.

I'd be more interested in those kinds of benchmarks than in the kinds of micro-benchmarks that just compare the speed of D allocation with the speed of C++ allocation.

--benji

%u wrote:
> "Do you have any observations about what shorts of things put you
> in the 20% category?"
> 
> - Luckly the code requiring sheer processing power like math
> functions(trigs, logs...), b-tree creation, compression, D code
> runs only 5-6% slower (an averaged mean) compared to Intel C
> compiler.
> - Unfortunately, processes requiring sheer memory access like
> memcopy, mem alloc, de-alloc, stream copy is nearly almost 15->20%
> slower at D. (note that, code is totally identical).

Some of this may be related to DMC's C library implementation vs. Intel's.  Could you try the app using DMC and compare it to DMD?


Sean

== Quote from Bill Baxter (wbaxter@gmail.com)'s article
> Teoman Soygul wrote:
> > My personal benchmarks prove that applications written in D
are 5%
> > to 20% slower than identical code written in C and compiled
with
> > Intel C compilter 9. Does anyone know what to do with this problem? Is it a compiler specific problem (ie: D compiler
lacking
> > all the optimisation parameters) or the standard d libary or what??
> >
> > Any information/idea would be appriciated. Before starting a
big
> > project, speed issues with D seems to be the biggest obstacle
to
> > overcome.
> >
> > Teoman Soygul,
> > Alsoft.
> One thing you might want to do is to also compare with C code
compiled
> using the Digital Mars C compiler since dmd and dmc use the same
back
> end.  This should help clarify what's due to inherent
differences in the
> languages and what's just differences in compiler optimization. --bb

Comparing Digital Mars C to Intel C really is a good idea to see if the performance difference is about D & C or D compiler and C compiler. I'll do that comparison also and post it so we can evaluate.

%u wrote:
> "Do you have any observations about what shorts of things put you
> in the 20% category?"
> 
> - Luckly the code requiring sheer processing power like math
> functions(trigs, logs...), b-tree creation, compression, D code
> runs only 5-6% slower (an averaged mean) compared to Intel C
> compiler.
> - Unfortunately, processes requiring sheer memory access like
> memcopy, mem alloc, de-alloc, stream copy is nearly almost 15->20%
> slower at D. (note that, code is totally identical).
> 
> I'll post these results on my blog once I put them into a good
> graphed format so we can discuss it even further. with my limited
> knowledge on compilers, what i've seen is that intel c compiler
> has many ingenious optimisations. maybe there can be a way to put
> the same ideas into D compiler. (i hope)


so are we talking about a GC issue? I think it would be interesting to use D for a front end to C . Then basically D code could be ran through the Intel optimizer.