More justification for this... Not inlining the handles would be like invokevirtual not emitting its type check inline and doing that as a separate CALL. Handles are our way to tell the JVM what native operations go with an invokedynamic. Not emitting those operations unconditionally into the compiled code treats invokedynamic as a second class citizen. Fair to say?
- Charlie (mobile) On Oct 17, 2011 11:52 AM, "Charles Oliver Nutter" <head...@headius.com> wrote: > Yeah that does sound like the right approach the more I think about it. The > invokedynamic operation and the handles that wire it up should never be > separated. Pathology aside, I know the JRuby logic would remain pretty small > in almost every case. And pathological cases could be detected with some > kind of MH graph-walking calculation (with a suitably large budget since > handles individually are maybe a couple native operations each). > > Let me know if you want me to test something out. I *really* hope this can > get into u2. > > - Charlie (mobile) > On Oct 17, 2011 9:28 AM, "Christian Thalinger" < > christian.thalin...@oracle.com> wrote: > >> >> On Oct 17, 2011, at 4:14 PM, Charles Oliver Nutter wrote: >> >> Yeah that's a pretty big problem :) Indy almost becomes a nonstarter if >> these degraded cases are not made a lot better. The performance on this >> example becomes terrible, and it's common for Ruby methods to be larger and >> more complex than this, too. >> >> Yeah, I know. >> >> You say you don't know how to fix it, so perhaps we can brainstorm a bit? >> If we can't inline the call we ate least want it to perform like an >> uninlined method call. Could we still compile the MH chain and CALL it, so >> at least we're not doing c2i? Or perhaps we should always treat the MH chain >> as inlinable regardless of budgets, but not inline the eventual call when >> budgets are exceeded? The latter option sounds more correct to me; the MH >> chain should be considered a non-removable part of the invokedynamic >> operation and always inlined. That would avoid the degradation without >> blowing up code size. >> >> I didn't say I don't know how to fix it but rather what's the best >> approach. Internally we (Tom, John and I) already talked about this and I >> tried to do something what you suggest above: compile the MH chain and call >> it. It turned out it's not that easy (as I thought) and needs some special >> handling. >> >> An interesting idea is to always inline the "adaption" code of the MH >> chain but not the eventual call (or all calls in the chain). I would guess >> that for normal usage the added code size is insignificant but there can >> definitely be pathological cases. I try to get some data on that. >> >> -- Chris >> >> - Charlie (mobile) >> On Oct 17, 2011 4:58 AM, "Christian Thalinger" < >> christian.thalin...@oracle.com> wrote: >> >>> >>> On Oct 15, 2011, at 2:56 PM, Charles Oliver Nutter wrote: >>> >>> > I'm seeing something peculiar and wanted to run it by you folks. >>> > >>> > There are a few values that JRuby's compiler had previously been >>> > loading from instance fields every time they're needed. Specifically, >>> > fields like ThreadContext.runtime (the current JRuby runtime), >>> > Ruby.falseObject, Ruby.trueObject, Ruby.nilObject (false, true, and >>> > nil values). I figured I'd make a quick change today and have those >>> > instead be constant method handles bound into a mutable call site. >>> > >>> > Unfortunately, performance seems to be worse. >>> > >>> > The logic works like this: >>> > >>> > * ThreadContext is loaded to stack >>> > * invokedynamic, bootstrap just wires up an initialization method into >>> > a MutableCallSite >>> > * initialization method rebinds call site forever to a constant method >>> > handle pointing at the value (runtime/true/false/nil objects) >>> > >>> > My expectation was that this would be at least no slower (and >>> > potentially a tiny bit faster) but also less bytecode (in the case of >>> > true/false/nil, it was previously doing >>> > ThreadContext.runtime.getNil()/getTrue()/getFalse()). It seems like >>> > it's actually slower than walking those references, though, and I'm >>> > not sure why. >>> > >>> > Here's a couple of the scenarios in diff form showing bytecode before >>> > and bytecode after: >>> > >>> > Loading "runtime" >>> > >>> > ALOAD 1 >>> > - GETFIELD org/jruby/runtime/ThreadContext.runtime : >>> Lorg/jruby/Ruby; >>> > + INVOKEDYNAMIC getRuntime >>> > (Lorg/jruby/runtime/ThreadContext;)Lorg/jruby/Ruby; >>> > >>> [org/jruby/runtime/invokedynamic/InvokeDynamicSupport.getObjectBootstrap(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/St >>> > ring;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite; (6)] >>> > >>> > Loading "false" >>> > >>> > ALOAD 1 >>> > - GETFIELD org/jruby/runtime/ThreadContext.runtime : >>> Lorg/jruby/Ruby; >>> > - INVOKEVIRTUAL org/jruby/Ruby.getFalse ()Lorg/jruby/RubyBoolean; >>> > + INVOKEDYNAMIC getFalse >>> > (Lorg/jruby/runtime/ThreadContext;)Lorg/jruby/RubyBoolean; >>> > >>> [org/jruby/runtime/invokedynamic/InvokeDynamicSupport.getObjectBootstrap(Ljava/lang/invoke/MethodHandles$Lookup;Ljava/lang/String;Ljava/lang/invoke/MethodType;)Ljava/lang/invoke/CallSite; >>> > (6)] >>> > >>> > I think because these are now seen as invocations, I'm hitting some >>> > inlining budget limit I didn't hit before (and which isn't being >>> > properly discounted). The benchmark I'm seeing degrade is >>> > bench/language/bench_flip.rb, and it's a pretty significant >>> > degradation. Only the "heap" version shows the degradation, and it >>> > definitely does have more bytecode...but the bytecode with my patch >>> > differs only in the way these values are being accessed, as shown in >>> > the diffs above. >>> > >>> > Before: >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 0.951000 0.000000 >>> > 0.951000 ( 0.910000) >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 0.705000 0.000000 >>> > 0.705000 ( 0.705000) >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 0.688000 0.000000 >>> > 0.688000 ( 0.688000) >>> > user system >>> > total real >>> > >>> > After: >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 2.350000 0.000000 >>> > 2.350000 ( 2.284000) >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 2.128000 0.000000 >>> > 2.128000 ( 2.128000) >>> > user system >>> > total real >>> > 1m x10 while (a)..(!a) (heap) 2.115000 0.000000 >>> > 2.115000 ( 2.116000) >>> > user system >>> > total real >>> > >>> > You can see the degradation is pretty bad. >>> > >>> > I'm concerned because I had hoped that invokedynamic + mutable call >>> > site + constant handle would always be faster than a field >>> > access...since it avoids excessive field accesses and makes it >>> > possible for Hotspot to fold those constants away. What's going on >>> > here? >>> >>> I looked into this and the main issue here is an old friend: slow >>> invokes of non-inlined MH call sites. The problem is that you trade a >>> normal invoke (to a field load?) with a MH invoke. If the normal invoke >>> doesn't get inlined we're good but if the MH invoke doesn't get inlined >>> we're screwed (since we are still doing the C2I-I2C dance). >>> >>> I refactored the benchmark a little (moved stack and heap loops into its >>> own methods and only do 5 while-loops instead of 11; that inlines all calls >>> in that method) and the performance is like you had expected (a little >>> faster): >>> >>> 32-bit: >>> >>> before: >>> >>> 1m x10 while (a)..(!a) (stack) 0.214000 0.000000 0.214000 >>> ( 0.214000) >>> 1m x10 while (a)..(!a) (heap) 0.249000 0.000000 0.249000 >>> ( 0.250000) >>> >>> after: >>> >>> 1m x10 while (a)..(!a) (stack) 0.203000 0.000000 0.203000 >>> ( 0.203000) >>> 1m x10 while (a)..(!a) (heap) 0.234000 0.000000 0.234000 >>> ( 0.234000) >>> >>> 64-bit: >>> >>> before: >>> >>> 1m x10 while (a)..(!a) (stack) 0.248000 0.000000 0.248000 >>> ( 0.248000) >>> 1m x10 while (a)..(!a) (heap) 0.257000 0.000000 0.257000 >>> ( 0.257000) >>> >>> after: >>> >>> 1m x10 while (a)..(!a) (stack) 0.226000 0.000000 0.226000 >>> ( 0.226000) >>> 1m x10 while (a)..(!a) (heap) 0.244000 0.000000 0.244000 >>> ( 0.244000) >>> >>> We have to fix that but I'm not sure yet what's the best approach. Sorry >>> I don't have better news for now. >>> >>> -- Chris >>> >>> > >>> > Patch for the change (apply to JRuby master) is here: >>> > https://gist.github.com/955976b52b0c4e3f611e >>> > >>> > - Charlie >>> > _______________________________________________ >>> > mlvm-dev mailing list >>> > mlvm-dev@openjdk.java.net >>> > http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev >>> >>> _______________________________________________ >>> mlvm-dev mailing list >>> mlvm-dev@openjdk.java.net >>> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev >>> >> _______________________________________________ >> mlvm-dev mailing list >> mlvm-dev@openjdk.java.net >> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev >> >> >> >> _______________________________________________ >> mlvm-dev mailing list >> mlvm-dev@openjdk.java.net >> http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev >> >>
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