After experimenting with MethodHandles.collectArguments (given a hand-written collector function) versus my own logic (using folds and permutes to call my collector), I can confirm that both are roughly equivalent and better than MethodHandle.asCollector.
The benchmark linked below calls a lightweight core Ruby method (Array#dig) that only accepts an IRubyObject (so all arities must box). The performance of collectArguments is substantially better than asCollector. https://gist.github.com/headius/28343b8c393e76c717314af57089848d I do not believe this should be so. The logic for asCollector should be able to gather up Object subtypes into an Object subtype without an intermediate array or extra copying. On Thu, Mar 25, 2021 at 7:39 PM Charles Oliver Nutter <head...@headius.com> wrote: > > Well it only took me five years to circle back to this but I can > confirm it is just as bad now as it ever was. And it is definitely due > to collecting a single type. > > I will provide whatever folks need to investigate but it is pretty > straightforward. When asking for asCollector of a non-Object type, > the implementation will first gather arguments into an Object, and > then create a copy of that array as the correct type. So two arrays > are created, values are copied twice. > > I can see this quite clearly in the assembly after letting things > optimize. A new Object is created and populated, and then a second > array of the correct type is created followed by an arraycopy > operation. > > I am once again backing off using asCollector directly to instead > provide my own array-construction collector. > > Should be easy to reproduce the perf issues simply by doing an > asCollector that results in some subtype of Object. > > On Thu, Jan 14, 2016 at 8:18 PM Charles Oliver Nutter > <head...@headius.com> wrote: > > > > Thanks Duncan. I will try to look under the covers this evening. > > > > - Charlie (mobile) > > > > On Jan 14, 2016 14:39, "MacGregor, Duncan (GE Energy Management)" > > <duncan.macgre...@ge.com> wrote: > >> > >> On 11/01/2016, 11:27, "mlvm-dev on behalf of MacGregor, Duncan (GE Energy > >> Management)" <mlvm-dev-boun...@openjdk.java.net on behalf of > >> duncan.macgre...@ge.com> wrote: > >> > >> >On 11/01/2016, 03:16, "mlvm-dev on behalf of Charles Oliver Nutter" > >> ><mlvm-dev-boun...@openjdk.java.net on behalf of head...@headius.com> > >> >wrote: > >> >... > >> >>With asCollector: 16-17s per iteration > >> >> > >> >>With hand-written array construction: 7-8s per iteration > >> >> > >> >>A sampling profile only shows my Ruby code as the top items, and an > >> >>allocation trace shows Object as the number one object being > >> >>created...not IRubyObject. Could that be the reason it's slower? > >> >>Some type trickery messing with optimization? > >> >> > >> >>This is very unfortunate because there's no other general-purpose way > >> >>to collect arguments in a handle chain. > >> > > >> >I haven¹t done any comparative benchmarks in that area for a while, but > >> >collecting a single argument is a pretty common pattern in the Magik code, > >> >and I had not seen any substantial difference when we last touched that > >> >area. However we are collecting to plain Object so it might be that is > >> >the reason for the difference. If I¹ve got time later this week I¹ll do > >> >some experimenting and check what the current situation is. > >> > >> Okay, I’ve now had a chance to try this in with our language benchmarks > >> and can’t see any significant difference between a hand crafted method and > >> asCOllector, but we are dealing with Object and Object, so it might be > >> something to do with additional casting. > >> > >> Duncan. > >> > >> _______________________________________________ > >> mlvm-dev mailing list > >> email@example.com > >> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev _______________________________________________ mlvm-dev mailing list firstname.lastname@example.org https://mail.openjdk.java.net/mailman/listinfo/mlvm-dev