6 ms·

Heh ... one of my employees took it into their head to code up some arithmetic algorithms in C++ a month or so ago. We do not use C++ for anything, we are all P

by zmmmmm 8y ago

Heh ... one of my employees took it into their head to code up some arithmetic algorithms in C++ a month or so ago. We do not use C++ for anything, we are all Python and JVM based. But he decided that he was going to achieve an amazing win by optimising some numerical code to get order of magnitude benefits, and without asking invested 4 hours into coding it up. I wrote a naive implementation of the same thing in Groovy, of all languages. My implementation was initially 20 times as fast and I coded it in 30 minutes. So he debugged some more and figured out that he misunderstood some of the inner workings of how vectors copy data and also that he did not understand the threading library he was using properly. He then fixed those two things. After this further exercise he reduced the difference to factor of 4. However he was never able to work out why my code was 4 times as fast as his C++ and abandoned it. I know for sure that with appropriate expertise the C++ could probably be made to go perhaps twice as fast as my Groovy code. But the point is, none of the supposed benefits come automatically regardless what language you are using. And unless you flip over to GPU or FPGA accelerated methods, the final outcome is well and truly in the same ballpark anyway. But all this is to say that "rarely translated" might be true at the for applications that are completely in the high performance domain. But for all the applications where the high performance code is in niches at the edge and there simply aren't resources or expertise to fully tune the native implementation ... I think it's translated all the time.

mynegation 8y ago
This is exactly it: dynamic languages give you OK ish performance and fast development speed. Fast C++ code requires a lot of expertise, this kind of expertise is expensive and there are diminishing returns too. I don’t know anything about expertise of your colleague in C++ but given that their first optimization was to eliminate some redundant copying, I suspect there is some more room for improvement. After unnecessary copying is removed it usually boils down to things like cache locality, better memory allocation discipline, data alignment, and sometimes knowledge of a better algorithm applicable to a particular situation (eg radix sort or perfect hashing or tries), judicial use of multi threading (in form of OpenMP), understanding whether single precision floating point is good enough etc etc.
- weberc2 8y ago
  I don’t think this is a property of dynamic languages. This groovy example is almost certainly the best case for the JVM (arithmetic, few allocations or polymorphism, etc). In other words, probably not taking advantage of the dynamism. Dynamic languages can be fast by being well designed and simple (Wren) or highly optimized (JS) or both (LuaJIT). There’s also the experimental GraalVM, but this is definitely the exception and not the rule. Writing performant C++ is actually not hard if you have rudimentary C++ knowledge. That said, rudimentary C++ knowledge is a lot more expensive than rudimentary knowledge of other languages. But the options aren’t just dynamic languages vs C++; there’s a ton of middle ground with VM languages like Java and C# and native languages like Go. The first two aren’t much harder than dynamic languages and I find Go easier than any dynamic language I’ve used to date (I’m a professional python developer). But all of these languages are on the order of half of C’s performance and 100X the speed of CPython or Ruby and 10X of JS.
  - pjmlp 8y ago
    > VM languages like Java and C# and native languages like Go. Oh well this VM meme is getting old, https://www.ptc.com/en/products/developer-tools/perc https://www.ptc.com/en/products/developer-tools/perc https://www.excelsiorjet.com/ https://www.excelsiorjet.com/ https://docs.microsoft.com/en-us/dotnet/framework/net-native/getting-started-with-net-native https://docs.microsoft.com/en-us/dotnet/framework/net-native... https://docs.microsoft.com/en-us/xamarin/mac/internals/aot https://docs.microsoft.com/en-us/xamarin/mac/internals/aot https://docs.unity3d.com/Manual/IL2CPP-HowItWorks.html https://docs.unity3d.com/Manual/IL2CPP-HowItWorks.html
    - weberc2 8y ago
      I don’t think I’m following your point. That C# isn’t a VM language because there exist AOT compilers? That’s fine; my point is unrelated to the VM/interpreter/AOT taxonomy—just that dynamic languages aren’t particularly performant. I’m happy to concede the “C# is/isn’t a VM (even though 99% of production deployments are VMs)” point if it matters to you.
physguy1123 8y ago
In my experience, writing java (or groovy here) in c++ results in horribly slow code which the jvm runs circles around, and it sounds like that's the problem your employee ran into. > But for all the applications where the high performance code is in niches at the edge and there simply aren't resources or expertise to fully tune the native implementation It's interesting you say this, because in my experience it's the JVM which requires absurd amounts of tuning and native programs which are much more consistent. The proper and easier way that native programs are written lends itself to fairly respectable performance, mostly because the object and stack model of say C or C++ is so much friendlier to the CPU than in most dynamic languages. In general, for all that I hear statements along this line, I've only twice seen code to back it up, and the C was so de-optimized from the OCaml version that I suspect it was intentional - the author (same for each) was a consultant for functional languages, and in one case switched the C inner loop to use indirect calls for every iteration and in the other switched the hash function between the C and functional comparison.
- shub 8y ago
  In addition, a lot of the techniques used to write high-performance Java boil down to "write it like C". Avoid interfaces, avoid polymorphic virtual calls (as you can't avoid virtuals entirely), avoid complex object graphs, avoid allocating as much as possible...it's not nearly as nice as naive Java. Still nicer than C IMO. If your process segfaults you can know for certain that it's a platform bug.
  - zmmmmm 8y ago
    The other thing that makes Java nicer than C is the ease and depth with which you can profile it to discover where the bottlenecks actually are. While it's certainly possible to profile in both cases, the runtime reflective and instrumentation capabilities of the JVM really add a lot of power to it.
- weberc2 8y ago
  It’s not native vs VM, but rather “has stack semantics/value types” vs “no stack semantics/value types”. In particular, OCaml’s standard implementation is a native, not VM. Also worth calling out Go, which is rather unique in that it has stack semantics but it also has a garbage collector, so it’s kind of the best of both worlds in terms of ease of writing correct, performant code.
tom_ 8y ago
Oh blimey, four hours...
blub 8y ago
Are you going to let your employees get away with investing all of 4 hours into things you did not give them permission for? You haven't shown them who the alpha is until they ask you for permission to go to the bathroom.

by zmmmmm 8y ago

mynegation 8y ago

This is exactly it: dynamic languages give you OK ish performance and fast development speed. Fast C++ code requires a lot of expertise, this kind of expertise is expensive and there are diminishing returns too. I don’t know anything about expertise of your colleague in C++ but given that their first optimization was to eliminate some redundant copying, I suspect there is some more room for improvement. After unnecessary copying is removed it usually boils down to things like cache locality, better memory allocation discipline, data alignment, and sometimes knowledge of a better algorithm applicable to a particular situation (eg radix sort or perfect hashing or tries), judicial use of multi threading (in form of OpenMP), understanding whether single precision floating point is good enough etc etc.

weberc2 8y ago
I don’t think this is a property of dynamic languages. This groovy example is almost certainly the best case for the JVM (arithmetic, few allocations or polymorphism, etc). In other words, probably not taking advantage of the dynamism. Dynamic languages can be fast by being well designed and simple (Wren) or highly optimized (JS) or both (LuaJIT). There’s also the experimental GraalVM, but this is definitely the exception and not the rule. Writing performant C++ is actually not hard if you have rudimentary C++ knowledge. That said, rudimentary C++ knowledge is a lot more expensive than rudimentary knowledge of other languages. But the options aren’t just dynamic languages vs C++; there’s a ton of middle ground with VM languages like Java and C# and native languages like Go. The first two aren’t much harder than dynamic languages and I find Go easier than any dynamic language I’ve used to date (I’m a professional python developer). But all of these languages are on the order of half of C’s performance and 100X the speed of CPython or Ruby and 10X of JS.
- pjmlp 8y ago
  > VM languages like Java and C# and native languages like Go. Oh well this VM meme is getting old, https://www.ptc.com/en/products/developer-tools/perc https://www.ptc.com/en/products/developer-tools/perc https://www.excelsiorjet.com/ https://www.excelsiorjet.com/ https://docs.microsoft.com/en-us/dotnet/framework/net-native/getting-started-with-net-native https://docs.microsoft.com/en-us/dotnet/framework/net-native... https://docs.microsoft.com/en-us/xamarin/mac/internals/aot https://docs.microsoft.com/en-us/xamarin/mac/internals/aot https://docs.unity3d.com/Manual/IL2CPP-HowItWorks.html https://docs.unity3d.com/Manual/IL2CPP-HowItWorks.html
  - weberc2 8y ago
    I don’t think I’m following your point. That C# isn’t a VM language because there exist AOT compilers? That’s fine; my point is unrelated to the VM/interpreter/AOT taxonomy—just that dynamic languages aren’t particularly performant. I’m happy to concede the “C# is/isn’t a VM (even though 99% of production deployments are VMs)” point if it matters to you.

physguy1123 8y ago

In my experience, writing java (or groovy here) in c++ results in horribly slow code which the jvm runs circles around, and it sounds like that's the problem your employee ran into. > But for all the applications where the high performance code is in niches at the edge and there simply aren't resources or expertise to fully tune the native implementation It's interesting you say this, because in my experience it's the JVM which requires absurd amounts of tuning and native programs which are much more consistent. The proper and easier way that native programs are written lends itself to fairly respectable performance, mostly because the object and stack model of say C or C++ is so much friendlier to the CPU than in most dynamic languages. In general, for all that I hear statements along this line, I've only twice seen code to back it up, and the C was so de-optimized from the OCaml version that I suspect it was intentional - the author (same for each) was a consultant for functional languages, and in one case switched the C inner loop to use indirect calls for every iteration and in the other switched the hash function between the C and functional comparison.

shub 8y ago
In addition, a lot of the techniques used to write high-performance Java boil down to "write it like C". Avoid interfaces, avoid polymorphic virtual calls (as you can't avoid virtuals entirely), avoid complex object graphs, avoid allocating as much as possible...it's not nearly as nice as naive Java. Still nicer than C IMO. If your process segfaults you can know for certain that it's a platform bug.
- zmmmmm 8y ago
  The other thing that makes Java nicer than C is the ease and depth with which you can profile it to discover where the bottlenecks actually are. While it's certainly possible to profile in both cases, the runtime reflective and instrumentation capabilities of the JVM really add a lot of power to it.
weberc2 8y ago
It’s not native vs VM, but rather “has stack semantics/value types” vs “no stack semantics/value types”. In particular, OCaml’s standard implementation is a native, not VM. Also worth calling out Go, which is rather unique in that it has stack semantics but it also has a garbage collector, so it’s kind of the best of both worlds in terms of ease of writing correct, performant code.

tom_ 8y ago

Oh blimey, four hours...

blub 8y ago

Are you going to let your employees get away with investing all of 4 hours into things you did not give them permission for? You haven't shown them who the alpha is until they ask you for permission to go to the bathroom.