[Manishearth]

That's a ... very small difference. And again, probably due to implementation differences. I'm not claiming C doesn't beat Rust, I'm just saying by very little -- Rust is practically just as fast, within the margin of error that microbenchmarks have. You have been belting out claims that Rust is 2x slower -- clearly false. Rust may be 5% slower -- which ... doesn't really matter.

Look at wycats' talk on fast_blank. That's a real world example that's faster than C. Rust used to be faster than c on the regex benchmark at one point, as burntsushi pointed out.

[bjourne]

> That's a ... very small difference. And again, probably due to implementation differences.

735 / 618 = 1.19 So Rust is at least 19% slower than C even without involving SIMD intrinsics. You wrote "your rust code shouldn't have any more overhead" but in all the benchmarks it has!

> You have been belting out claims that Rust is 2x slower -- clearly false.

Clearly not, since it is on all the SIMD-using benchmarks.

> Look at wycats' talk on fast_blank. That's a real world example that's faster than C. Rust used to be faster than c on the regex benchmark at one point, as burntsushi pointed out.

Because it is comparing different regex engines, not language performance. I said you should apply "common sense" to The Benchmark Game's numbers.

Here's the thing, you guys can easily prove me wrong. Prove that Rust has zero cost abstractions by taking any small C benchmark, transliterate it to Rust code and profile it. If it is as fast, I'm proven wrong. If it is slower you are proven wrong.

[Manishearth]

Rust can use simd too. It doesn't in those benchmarks. Please apply the common sense you keep harping about. Claiming rust is 2x slower because of that benchmark is a falsehood.

Re:regex: my point exactly. Most microbenchmarks are prone to slight differences in the implementation causing issues (and you can rarely translate code exactly, especially to something like rust which often requires a different structure of code from C. Same for any two other langauges). 19% is well within this error box.

The fast_blank thing is this example. fast_blank is a carefully hand optimized C extension whose main purpose is being super fast. A mostly naive Rust one-liner beat it (not by much iirc, perhaps 10%, but thats within the error box im talking about). It didn't use parallelism or anything fancy. They weren't even trying to beat C. I provided this proof already.

I could try fixing that benchmark you linked to -- the rust version looks like it could be optimized further. Not sure if its worth it, really. I don't put much stock in microbenchmarks for anything other than order of magnitude comparisons.

[bjourne]

> Rust can use simd too.

No it can't. Either accept that the nightly build of Rust is not the Rust we are talking about or stop discussing with me.

> Re:regex: my point exactly.

The problem with regex libraries are that they are to big so therefore doesn't reveal so much about inherent language performance.

> Most microbenchmarks are prone to slight differences in the implementation causing issues (and you can rarely translate code exactly, especially to something like rust which often requires a different structure of code from C. Same for any two other langauges).

Yes, obviously the implementation defines performance. That's what I wrote in the other thread part: "this discussion is about Rust vs C. Or rather clang 3.6.2/gcc 5.2.1 vs Rust 1.9.0 since language performance is very implementation dependent"

And fwiw, you can easily transliterate C code to C++ or to asm.

> 19% is well within this error box.

What error box? 19% is a huge difference.

> The fast_blank thing is this example. fast_blank is a carefully hand optimized C extension whose main purpose is being super fast.

I don't know what fast_blank is. Is it this https://github.com/SamSaffron/fast_blank/blob/master/ext/fas... C code wycatz managed to rewrite faster in Rust? That C code isn't well-optimized at all...

> I don't put much stock in microbenchmarks for anything other than order of magnitude comparisons.

Does that mean it is impossible to prove to you that C is at least 2x faster than Rust since twice is less than one order of magnitude?

[Manishearth]

What's nightly in Rust today will become stable soon enough (idk the timeline for SIMD). But OK. Stable only. In that case, rust is 2x slower than c code that can be optimized by SIMD. Not much of an issue, really, and it proves nothing about rusts overhead except that you can't rely on autovectorization. Not really a big deal.

> 19% is a huge difference.

IMO that in the realm of microbenchmarks, it really isn't. You clearly disagree, not much I can do about that.

> That C code isn't well-optimized at all...

Go ahead and fix it then. You've been telling me much the same. I already mentioned that the other benchmark you linked me to wasn't optimized.

> Does that mean it is impossible to prove to you that C is at least 2x faster than Rust since twice is less than one order of magnitude

I use the term loosely, 2x is certainly alarming. As long as you rely on simd benchmarks I will disagree though, since in most cases a lack of that optimization isn't the reason your program is slow. If you really really care about performance, use nightly rust; there's no cost to that. I have yet to see production C code that uses SIMD everywhere possible, just in some tight loops. That is not going to create a 2x difference in performance unless the tight loop dominates all else. That is not most use cases.

[bjourne]

> Not much of an issue, really, and it proves nothing about rusts overhead except that you can't rely on autovectorization.

Not much of an issue unless you actually need the performace ofcourse. Ime, simd intrinsics is everywhere in code optimized to run as quickly as possible on x86. That about half of The Benchmark Game's benchmarks uses sse proves that point.

> Go ahead and fix it then. You've been telling me much the same. I already mentioned that the other benchmark you linked me to wasn't optimized.

That requires investing a lot of time in understanding how Ruby's internals and especially its string objects works. I don't have that time. The LPathBench on the other hand is self-contained and updating it shouldn't be more than a few hours of work for a decent Rust programmer.

[Manishearth]

> Not much of an issue unless you actually need the performace ofcourse. Ime, simd intrinsics is everywhere in code optimized to run as quickly as possible on x86. That about half of The Benchmark Game's benchmarks uses sse proves that point.

My point is that the Benchmark Game is not representative of real world code. The website says as much. Because the benchmarks use sse everywhere does not mean that most code, even perf-sensitive code will use simd everywhere.

Again, if you need simd, use a nightly. There's little to no drawback there.

I fixed it up to run on modern rust (https://gist.github.com/Manishearth/5fc73c405641162f0712951c..., compile with cargo build --release), and the numbers I get are:

(Ranges are just what I got from 5 runs, nothing scientific)

Rust: 610-630

c: 706-716

c_fast: 919?

cpp_clang: 669-694

cpp_plain: 717-728

I'm on a new (i7, 16gb) Mac so I don't yet have g++ around (nor do I know how to obtain it without messing things up; I'm used to linux), everything here done with clang.

Of course, this isn't an indication that Rust is faster than C. But it is an indication that it can be just as fast, and a reinforcement of my point about microbenchmarks having large error bars.

Edit:

On my older x86 linux laptop (with gcc):

Rust: 844-987

c_fast: 808-860 (perhaps clang somehow made c_fast slower than c on the mac? shrug)

c: 982-1025

cpp_plain: 977-1019

cpp_gcc: 925-947

I think I've proven my point.

[Manishearth]

Oh, and transliterating C and C++ is an exception to the norm. C and C++ are historically linked and quite similar in many ways. Rust does not have this relationship with C. You could easily transliterate C code to unsafe rust code, but that sort of misses the point, doesn't it? :)

[burntsushi]

> Because it is comparing different regex engines, not language performance. I said you should apply "common sense" to The Benchmark Game's numbers.

Then don't also use regex-dna as evidence that Rust is "slow":

> Rust is also slower in binarytrees, regexdna and fasta.

You can't have it both ways.