Date: Fri, 13 Sep 2024 07:21:02 -0600 From: Alan Somers <asomers@freebsd.org> To: Jason Bacon <bacon4000@gmail.com> Cc: freebsd-hackers@freebsd.org Subject: Re: The Case for Rust (in any system) Message-ID: <CAOtMX2j4c9%2Br3vuwhm3k1EL3EL8BLrP8VWxBYmxPnWMvaDWcng@mail.gmail.com> In-Reply-To: <ce457b53-f1c2-4a95-917a-c17bcb1c81ed@gmail.com> References: <CAOzHqcJ0rOR4CoL84WgZQNcgY2G9vuiHccE4XT_otJ2R51KJ3Q@mail.gmail.com> <2EE309BF-CE1D-48AD-9C53-D4C87998B4A0@freebsd.org> <e12a3441-3143-426b-b921-7c3357ed4738@gmail.com> <ce457b53-f1c2-4a95-917a-c17bcb1c81ed@gmail.com>
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On Fri, Sep 13, 2024 at 7:15=E2=80=AFAM Jason Bacon <bacon4000@gmail.com> w= rote: > > On 9/13/24 05:33, Paul Floyd wrote: > > > > > > On 13-09-24 06:17, David Chisnall wrote: > >> On 13 Sep 2024, at 02:34, Joe Schaefer <joesuf4@gmail.com> wrote: > >>> > >>> I just completed a month long project to port a C++ codebase that > >>> used vectors for array allocations back to using C=E2=80=98s calloc. = For a > >>> 15% increase in memory footprint, batch jobs that took three days to > >>> complete now finish in 10-12 hours. > >> > >> This sounds highly dubious given that std::vector is a very thin > >> wrapper around malloc. From your description, I would expect the same > >> speedup with some judicial use of .reserve(). > > > > I was going to say exactly the same thing. > > > > Considering the reply to this, another one to be plonked so that I wast= e > > less time. > > > > A+ > > Paul > > > > > > > > Some years ago, I wrote a script to time a simple selection sort coded > in various languages. Here's an example of the results: > > https://github.com/outpaddling/Lang-speed/blob/master/Results/coral-amd64= -100000 > > Note: The clang array/pointer performance is currently regressed due to > changes in the optimization parameters since clang 8. That's why it's > noticeably slower than GCC in these results. > > https://github.com/llvm/llvm-project/issues/53205#issuecomment-2318697322 > > In general, I have not seen a significant difference between arrays and > vectors in all my years running this benchmark. > > This benchmark is anecdotal, as it only measures performance for one > algorithm. But in my experience, C++ shows marginally slower > performance and noticeably more memory use than C. > > Coming back to Rust: The results above, showing about double the runtime > of C and C++, is the best I've seen from it. It was taking 4x as long > as C/C++ a few years ago. That's one reason I don't use it. I do > mostly scientific computing, where runtime can be costly. This is not > *always* an issue in systems code, but it should be examined before > choosing a language for a particular implementation. The other reason > is the impact of a Rust dependency on FreeBSD ports and pkgsrc packages: > Frequent changes to the Rust port/package lead to long build times and > frequent breakage of dependents. Right away, I can see that while your C program mallocs the array to the list's full size, your Rust program doesn't. It grows the list one element at a time, with Vec::push . I bet that if you change the Rust program to use Vec::reserve or Vec::with_capacity, so that it only has to allocate once, you'll find the results are different. -Alan
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