Hey thanks! Contrary to popular belief, x86_64 assembler isn't really that bad to deal with. An eagle-eye perspective is simply that regardless of how good optimising compilers get, they can never really know my intent. My zlib implementation for example is consistently 25% faster than the reference version, despite me simply "hand compiling" it straight from the C source. There are lots of contributing factors that all add up to the end result as seen in the benchmarks.
The short answer is: there is no single reason, it is the culmination of all of the underlying bits of the library that made it what it is.
I added code profiling to rwasa so that you can run load tests against it and watch call graphs and individual function timings, which makes for interesting inspection of the library itself for specific "tricks" that were employed. (the library's page contains rwasa-specific profiling examples: https://2ton.com.au/HeavyThing/ )
> My zlib implementation for example is consistently 25% faster than the reference version, despite me simply "hand compiling" it straight from the C source.
I am aware of Intel's patch re: psubusw usage, and interestingly chose the same solution when hand-compiling it as theirs well before I saw their patch to it (in fill window, which does make a substantial difference).
Have you compared my code to [your?] repo yet? I will endeavour to do so, though I am not sure submitting a fasm-based patch to that repo would make sense. Cheers
Regarding zlib, is that the fastest implementation that's currently available?
I rememeber stumbling into a guy that claimed his implementation was way faster (2x or more) than the original zlib, and it was a drop-in replacement and scaled fairly well. Unfortunately, I can't find it right now (it should be bookmarked on another computer).
Various people have attempted to speed up zlib; it's not that high a bar, if you're OK with not producing output binary-identical to the original zlib. Deflate compression algorithms keep references to possible LZ backreferences in a hash table, and depending on your choice of hash algorithm, and how much you prune your table versus spending memory and time storing and searching it, you'll end up emitting different backreferences. The implementation at https://github.com/jtkukunas/zlib/ replaces the hash algorithm with something much faster.
libslz is really, really fast (and fairly new). It's used in the next version of haproxy. In my own tests it's proved substantially faster than both zlib and miniz.
> Contrary to popular belief, x86_64 assembler isn't really that bad to deal with.
I think most beliefs regarding x86_64 asembly is largely "guilt by association" with i386... It's amazing the difference just from making use of the larger register set.
It's the same in the high assurance systems field albeit with different goals. We're concerned with optimization-induced failures, subversion, complexity, and so on. Mainstream languages and their compilers... doesn't exactly help on this. I've been out of it a while, evangelizing & informing mainly these days. Yet, your post brings back memories.
My strategy, leveraging the Write Great Code book, was to map language constructs onto assembler via macro-assembler or languages such as LISP with good metaprogramming. Then, I hand compiled the code in other's projects with my macro's. So, we took a similar approach there although my goal was to show a correspondence argument between source & asm. Meta tools turned that into full program for assembling and linking.
One wild idea I had for portability was doing optimized routines of a safe HLL in a bytecode like LLVM. That knocks out most of the uncertainty of above layers that limit optimizations the most. Then, the simple optimizations that machines are good at can be performed from there along with generation of assembler. Close to portability of C and efficiency of hand-written assembler with inline available.
For instance, code zlib functions in pretty optimal LLVM and let toolchain do the rest on full-optimization. Think yours will be 25% faster, 10%, similar? And I'm talking what you can code quickly rather than spend 30min-1hr optimizing by hand. Just curious to hear your thoughts as you have way more experience in that stuff.
Saying that you're afraid by optimization-induced failures and then saying that you will feed some LLVM bytecode to the optimizer seems contradictory to me...
They're kind of two different things. The first was hand-compiling (or tracing) things for highly assured work. The other was a tangent where I wonder if a bytecode like LLVM could be used as a cross-platform assembler that's closer to hand-optimized assembler than C due to less knowledge of intent being required. Not to mention simpler structure.
They're different things. If it's a worthwhile path, then the formal efforts on LLVM IR and verified optimizations could be combined with hand-made, inline LLVM for a safer, portable alternative to different inline assembler for each platform. Complimentary, not contradictory, when in context.
Ah ok. Appreciate that detail. My concept was replacing inline assembler in an otherwise portable 3GL with LLVM bytecode. The compiler wouldve taken care of ABI in that scenario. LLVM should be easier to optimize than C and maybe fast enough to eliminate need for several different assemblers.
> My zlib implementation for example is consistently 25% faster than the reference version, despite me simply "hand compiling" it straight from the C source.
Yeah, but that is a very CPU bound processing pipeline. You would expect that to maximize the impact of any inefficiencies in the compiler.
That you can hand tune for better performance is conceivable. That you can get a 2x win over some pretty tuned code suggests that there is something larger at work than simply tuning lots of little things.
The short answer is: there is no single reason, it is the culmination of all of the underlying bits of the library that made it what it is.
I added code profiling to rwasa so that you can run load tests against it and watch call graphs and individual function timings, which makes for interesting inspection of the library itself for specific "tricks" that were employed. (the library's page contains rwasa-specific profiling examples: https://2ton.com.au/HeavyThing/ )