3 ms·

I wonder if the dalvik VM is optimized for regular computer architectures or only for the G1. Either way, I remember reading that Dalvik (or, well, Java) was c

I wonder if the dalvik VM is optimized for regular computer architectures or only for the G1. Either way, I remember reading that Dalvik (or, well, Java) was chosen for the constraints it places on the programmer and access to verification tools? Security or some such?

michaelneale 18y ago
Dalvik is register based byte code - from what little I have looked at it - it looks quite low level and apparently it is meant to run fast enough "interpreted" (ie a JIT isn't practical on small devices). However JVM bytecode (and similar) being stack based is much higher level, leaving more room for JITs to make a faster runtime (but for some cost which is not practical on small devices) - but slower when "interpreted". At least that is my understanding.
- wmf 18y ago
  This is a good summary of the conventional wisdom, but I don't know if it's right. Phones are now about as powerful as PCs from ten years ago; IIRC we were using JITs on those PCs. Is Dalvik really "fast enough"? If, say, 5x more performance was available, would developers not use it?
  - michaelneale 18y ago
    hmm... 10 years ago I don't remember thinking that fondly of JITed runtimes - sure they worked in a server context with long running apps that had time to warm up, but not so much on the desktop. I guess its a tradeoff - to a user a JITed app would appear a bit slow at first, but get faster the more you use it (plus you would then need to probably persist the JIT codes, as you close/open apps all the time in android) which has more complexity. A fast runtime like dalvik is the same speed pretty much all the time. Yes, it is conventional wisdom, but I am not sure if phones are as fast as we think yet. Sure my iphone runs at what, 450Mhz ? which is quick, but we may forget that JIT'ing of client side apps only recently became fast enough (at least to my taste).
  - litewulf 18y ago
    Many phones don't run at their full CPU speed to save battery power...

michaelneale 18y ago

Dalvik is register based byte code - from what little I have looked at it - it looks quite low level and apparently it is meant to run fast enough "interpreted" (ie a JIT isn't practical on small devices). However JVM bytecode (and similar) being stack based is much higher level, leaving more room for JITs to make a faster runtime (but for some cost which is not practical on small devices) - but slower when "interpreted". At least that is my understanding.

wmf 18y ago
This is a good summary of the conventional wisdom, but I don't know if it's right. Phones are now about as powerful as PCs from ten years ago; IIRC we were using JITs on those PCs. Is Dalvik really "fast enough"? If, say, 5x more performance was available, would developers not use it?
- michaelneale 18y ago
  hmm... 10 years ago I don't remember thinking that fondly of JITed runtimes - sure they worked in a server context with long running apps that had time to warm up, but not so much on the desktop. I guess its a tradeoff - to a user a JITed app would appear a bit slow at first, but get faster the more you use it (plus you would then need to probably persist the JIT codes, as you close/open apps all the time in android) which has more complexity. A fast runtime like dalvik is the same speed pretty much all the time. Yes, it is conventional wisdom, but I am not sure if phones are as fast as we think yet. Sure my iphone runs at what, 450Mhz ? which is quick, but we may forget that JIT'ing of client side apps only recently became fast enough (at least to my taste).
- litewulf 18y ago
  Many phones don't run at their full CPU speed to save battery power...