----- Mail original ----- > De: "Vladimir Ivanov" <vladimir.x.iva...@oracle.com> > À: "Jochen Theodorou" <blackd...@gmx.org>, "Da Vinci Machine Project" > <mlvm-dev@openjdk.java.net> > Envoyé: Lundi 19 Février 2018 15:47:45 > Objet: Re: Why is LambdaMetafactory 10% slower than a static MethodHandle but > 80% faster than a non-static MethodHandle?
> On 2/19/18 5:13 PM, Jochen Theodorou wrote: >> On 19.02.2018 14:31, Vladimir Ivanov wrote: >> [...] >>> CallSites are the best you can get (JITs treat CallSite.target as >>> constant and aggressively inlines through them), but you have to bind >>> CallSite instance either to invokedynamic call site or put it into >>> static final field. >> >> And that really extends to MutableCallsite? In a dynamic language where >> you depend on the instance types you cannot do all that much with a >> non-mutable callsite. > > Yes, it covers all flavors of CallSites. In case of > Mutable/VolatileCallSite, JIT-compiler records a dependency on CallSite > target value and invalidates all dependent nmethods when CallSite target > changes. It doesn't induce any overhead at runtime and allows to reach > peak performance after every CallSite change (due to recompilation), but > it doesn't favor regularly changing CallSites (manifests as continuous > recompilations at runtime). For the shake of completeness, i will just add that this is only true for callsites that are attached to a bytecode, i.e. the ones that are returned by a bootstrap method, if you allocate and store a CallSite in a local variable, it will not magically turn itself to a constant. And that the VM trusts you, i.e. if you mutate a MutableCallSite too frequently (by example at each call), it will be dog slow because the JIT will optimize/deoptimize at each call. > > Best regards, > Vladimir Ivanov > Rémi _______________________________________________ mlvm-dev mailing list mlvm-dev@openjdk.java.net http://mail.openjdk.java.net/mailman/listinfo/mlvm-dev
