On Monday, 18 July 2016 13:27:09 UTC+3, Michael Jones wrote: > > Anything much faster than this needs vector operations in the interpreter > so the “get to the OP function” overhead is once per time series rather > than once per element in the series. >
I managed to make it a little faster https://play.golang.org/p/Tr2PRKI23w, but runs only on windows (kind of). *What have I done...* + Egon > > > *From: *<golan...@googlegroups.com <javascript:>> on behalf of Egon < > egon...@gmail.com <javascript:>> > *Date: *Monday, July 18, 2016 at 1:32 AM > *To: *golang-nuts <golan...@googlegroups.com <javascript:>> > *Cc: *<ondrej...@gmail.com <javascript:>> > *Subject: *[go-nuts] Re: An efficient runtime expression evaluation > > > > > > On Monday, 18 July 2016 11:13:08 UTC+3, Egon wrote: > > > > On Monday, 18 July 2016 10:30:14 UTC+3, Egon wrote: > > On Monday, 18 July 2016 03:11:29 UTC+3, ondrej...@gmail.com wrote: > > Cheers, I tried replicating my endeavours ( > https://play.golang.org/p/Qxoo2ASac6), sorry if it's still too verbose. > It's essentially rewriting the inbuilt ast.Node into a simpler nested > struct and then walking it. > > > > In testing the performance, I started adding algebraic expressions, which > make my walking more expensive, but don't change the 'native' expression > evaluation (I guess due to constant folding). > > > > As to your suggestion three - I do the variable lookup in the parsing > stage, but I still need to retain the pointer, not the value itself, > because I'm accessing an element of that given variable (time series), and > this element (time period) changes at runtime. > > > > https://play.golang.org/p/dd4hTpMKrp > > > > Of course you can additionally add constant folding and similar... > Additionally instead of working on a single float at a time, make each > variable an array of 8 floats, that are computed in parallel. > > > > > > Just realized that it's trivial to write basic constant folding: > https://play.golang.org/p/iqWX5_Mweb > > > > Although it probably will be easier to maintain and extend as a separate > pass: https://play.golang.org/p/xcz5mXoaOG > > > > > > This brings the result to: > > > > interpreter: 17.001ms > > native: 7.0004ms > > > > Which is approximately the best I would expect from an interpreter without > JIT (and not computing multiple time-points at a time). > > > > + Egon > > > > One performance gain I can think of is to implement some pruning through > the abovementioned constant folding and other optimisations, but I'd rather > leave that as the last resort. Another thing that comes to mind is that I > could return nested closures in some way - meaning that '1+3*x' would be, > in go-like pseudocode, add(func() { return one }, func mul(func() { return > three}, func() {return model[x]} )), where the one/tree are values passed > to the closure when parsing the equation; but that's just now off the top > of my head. > > > > I attached a pprof result in the header. > > > > Thanks again. > > > On Friday, 8 July 2016 15:46:32 UTC+1, Egon wrote: > > On Friday, 8 July 2016 16:25:40 UTC+3, Ondrej wrote: > > Hi all, > > I have a model with variables, let's call them a, b, c, ..., z. These are > numerical values (time series loaded from a database) and I let the user > specify their relationships in a JSON, say 'z = 12; x = a + 2/3 + 3*c; y = > log(12*f) + exp(g)' etc. The syntax is trivial - it's basically just > algebraic relationships + a few functions (log, log2, log10, exp, > trigonometrics, ...; all 1:1 mappings to their math package equivalents). > > > > *Tip: include a working piece of code that you want to make faster, it > makes it easier for people to see the problems and common issues.* > > > > > > Now, I get these relationships in a JSON and I parse them using go/parser. > Then I walk the tree once and process it a bit - replacing keywords by > pointers to my variable stores, replacing all the log/exp/sin with function > pointers, leaving literals be literals etc. Each node is then a struct with > a type and the actual contents (sadly a generic interface, because the > value can be almost anything). The prep stage is now over. > > > > When actually running the model, I loop through years and within each year > I solve each variable - I walk the tree and evaluate it where needed. The > only non-trivial action is when I get to a model variable, I need to do a > bit of lookup (it's a time series, so I need to look up the correct time > period and other bits). Otherwise it's just literals, operators and > function calls, all of which is fairly straightforward. > > > > This is all well and good. One of the issues is that it's rather slow. I > thought it would be the recursive nature (and interface assertions), but > converting all this into a shunting yard system didn't improve the > performance dramatically. I've profiled the thing and removed a few > hotspots, my question is not about profiling. I'm after a bit more general > advice on how to handle these runtime evaluations and if there are better > ways of doing so. Essentially some sort of a JIT (but Go does not have > runtime assembly, right?), or maybe convert each expression into a closure > or maybe a whole different algorithm or...? > > > > Reduce the amount of code and indirection that you need to do, few basic > ideas: > > 1. implement a VM https://play.golang.org/p/dlmZ2lGPY7 > > 2. operate on vectors of variables instead of single values > https://play.golang.org/p/25MIjIXs0D > > 3. try to do the lookup of all necessary variables before starting to > compute with them; if possible > > > > Obviously pprof is your friend. ( > https://blog.golang.org/profiling-go-programs) > > > > + Egon > > -- > You received this message because you are subscribed to the Google Groups > "golang-nuts" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to golang-nuts...@googlegroups.com <javascript:>. > For more options, visit https://groups.google.com/d/optout. > > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
