Go vs. Swift vs. C++ microbenchmark

http://lionet.livejournal.com/137511.html

by monort • 10 years ago

63 36 10 years ago

lionet.livejournal.com

marvel_boy• 10 years ago

I'd love to see Erlang here. Anyway Swift performance is impressive.

DannyBee2• 10 years ago

Oh microbenchmarks.

All of this is going to be optimized away by a sufficiently smart compiler or a compiler you tell you want to spend lots of time optimizing.

In general: don't write microbenchmarks where the results can be easily statically evaluated by the compiler, unless you are testing whether the compiler can statically evaluate it (this is a reasonable thing to want to know of course, but it's not a test of the language).

There are also languages which will pretty much not bother to do a lot of the the actual work, like haskell.

(Note: In this case, the the C++ compiler being used actually knows all the recurrences involved, but decides it's too expensive to statically calculate the final result of sum. GCC would do the same.)

21• 10 years ago

Doesn't the std::vector calls mess things up? Now the compiler has to track those as well, they involve the allocator which calls into the OS.

So for the compiler to be able to statically compute the result it would need to know that the std::vector stuff doesn't have side effects.

Of course, the compiler could have special knowledge of std::vector, like for example in general it has about memcpy.

DannyBee2• 10 years ago

"So for the compiler to be able to statically compute the result it would need to know that the std::vector stuff doesn't have side effects. "

It can know this the same way it knows about memcpy.

Most of them have library call info for things that have standardized guarantees.

Even if it didn't, it knows what malloc does, it knows this variable never escapes, and ...

pjmlp2• 10 years ago

Not only that, usually all the ones applied via gut feeling instead of a profiler are meaninglessness.

Additionally, depending on the application domain, it might not even matter.

zeckalpha• 10 years ago

And Haskell, in the comments.

stepanhruda• 10 years ago

Concurrency model will be a big focus for Swift 4.

(Swift is currently v2.2, the focus of v3 is to stabilize the ABI.)

campoy2• 10 years ago

I don't care about micro benchmarks ... but if you're gonna do one, make sure your code is decent.

By replacing the Go slice declarations (var x[]int64) with (x := make([]int64, 0, 1000000)) you'll get an algorithm that in my iMac runs much faster:

- your version: 4.93s user 0.28s system 165% cpu 3.151 total

- my version: 1.93s user 0.04s system 168% cpu 1.165 total

EDIT: I'm sure this happens with all the examples, and that's exactly my point. What is this exactly microbenchmarking? Bad programs?

masklinn7• 10 years ago

(Re)allocating arrays/vectors seems to be pretty much the whole point, otherwise both Swift and C++ could not only preallocate (reserve), but they could use iterators and elide all allocation instead, and then you'd get something along the lines of this:

    > rustc -O test.rs -o test_rs
    > time ./test_rs
    9999010000
            0.54 real         0.53 user         0.00 sys

here's TFA's C++ version by comparison:

    > time ./test_cpp
    9999010000
            3.17 real         2.29 user         0.86 sys

campoy2• 10 years ago

I totally agree with you on this. The code for all three languages is clearly not optimal.

I wonder how much of this performance difference is C++ being very good at optimizing your code rather than the runtime being more performant. I don't have any numbers, but I feel like that's not a negligible factor.

azth• 10 years ago

Could you link to the code for `test.rs`?

imaginenore• 10 years ago

No, that breaks the fair comparison. Other language examples do not pre-allocate all the vectors.

tumdum_• 10 years ago

It is already broken ;)

In c++ indexing vector does no range checks while in Go indexing slice checks validity of index.

And vector in gcc growths by factor of 2 while slice in Go grows by 25% after it's bigger than 1024 elements. So there is a trade-of between memory usage and number of allocations.

And... I could go on, but the point is that microbenchmarks are in general not that useful :)

jasode2• 10 years ago

If the C++ version didn't use vector.reserve(1000000), what justifies the reason for the Golang version to use make(,,1000000)?

pella• 10 years ago

this case added to https://github.com/golang/go/issues/14325

jamra2• 10 years ago

The point is to sell Swift. In the C++ example, he didn't cast each integer to int64, but he manufactured a reason to do it in Go and Swift. Perhaps this means that Swift's compiler optimizes that particular case almost as good as Go's. It doesn't matter much because it's a single threaded useless benchmark. It's the kind of thing that can change with a new Go or Swift release. As you know better than I, Go slowed down a small amount when the recent GC optimizations were done. Is that a reason to use Go less? No. The GC is quite amazing (and there is HTTP2 support).

In general, why do I care if there are slight variations in the speed of a for loop? The bottleneck in any app is the database or network access. Maintenance and readability matter to me a lot more than minuscule variations in speed.

As someone who programs in Go and Swift, I can tell you that Swift has some things Go doesn't. For one, it has generics. Even still, I would likely never use it over Go on any code that runs on a server. This is due to readability and the Go standard library. I would still choose Swift over Go for iOS development. This is due to how the iOS stack is premised on object inheritance.

masklinn7• 10 years ago

The point is to sell Swift. In the C++ example, he didn't cast each integer to int64, but he manufactured a reason to do it in Go and Swift.

Wow, the crazy is strong with this one. The reason for the cast is that C++ follows C in implicitly converting between integer sizes but neither Swift nor Go do, remove the casts and the code doesn't compile:

    > swiftc -O test.swift -o test_swift
    test.swift:8:18: error: cannot convert value of type 'Int' to expected argument type 'Int64'
            x.append(i);

    > go build test.go
    # command-line-arguments
    ./test.go:12: cannot use i (type int) as type int64 in append

And while the correct fix was probably to type the loop variable as an int64 (which incidentally is ugly and non-obvious in Go, you have to convert one of the for loop's bounds to an int64 were Swift will just let you explicitly type the loop variable to Int64) it also changes jack shit to the runtime:

    > time ./test-go-type
    9999010000
    ./test-go-type  10.88s user 0.86s system 153% cpu 7.660 total

    > time ./test-go-cast
    9999010000
    ./test-go-cast  11.04s user 0.87s system 154% cpu 7.699 total

rurban• 10 years ago

If you want to compare fast languages, you need to compare C++ with rust and pony, not swift and go.

pjmlp2• 10 years ago

And include multiple implementations of each one, as that is what really counts.

oussama-gmd• 10 years ago

Where is Rust :)

jbeja2• 10 years ago

In academia.

bluejekyll• 10 years ago

This is totally unfair. We're looking at using Rust for production workloads and cross system development.

justinsb• 10 years ago

As far as micro-benchmarks go, this one is particularly egregious. It is likely completely dominated by the array reallocation. So a runtime that - say - chooses to preallocate an array at size 1000000, or to go to 1000000 at first resize would win at this benchmark. More realistically, a runtime that conserves memory by reallocating arrays with a 1.5x factor vs a 2x factor will appear slower.

It's exactly because you don't want to rely on the runtime making the right call for your use-case that you preallocate arrays where it makes a difference (i.e. where you're appending a million items).

And 99% of the time you're doing less than 100 items, and so the array reallocation behavior just doesn't matter.

0x434D53• 10 years ago

So what's the conclusion of this besides some useless numbers?

jbeja2• 10 years ago

What's the point, seriously?

autoreleasepool• 10 years ago

FYI, unary operators and C-style for loops have been depreciated in Swift.

jsksma2• 10 years ago

"But it adds some checks and GC, so Swift also exhibits a serious slowdown, though well within 2x of C++."

Swift does not employ GC, it uses ARC. While that may be a form of GC, it doesn't suffer from the same "slowdown" that GC would in this context because ARC is doing exactly what your base case (C++) does at run-time (ARC is a compile-time tool).

I think if you're going to be doing benchmarks, you should have basic knowledge on how each system works first.

chvid• 10 years ago

I really think this is mostly just testing how well the list/vector/array class is handling being asked to expand itself by one element a million times.

Go vs. Swift vs. C++ microbenchmark

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