3 ms·

Theoretically speaking, JITs have access to strictly more information than AOT, so they ought to be better once you amortize out the timing issues. A really goo

Theoretically speaking, JITs have access to strictly more information than AOT, so they ought to be better once you amortize out the timing issues. A really good profiling JIT will do a fast-compile pass the first time through, and then progressively re-compile with knowledge gained from profiling during runtime.

wredue 3y ago
“Has more information therefor better optimized” is bordering on a lie, is the problem. Theres truth to a point I guess, but it’s also true that lots of “more information” is useless, and sometimes harmful to optimization, and additionally that it’s really diminishing returns. Truth is as long as you’re not over relying on RAII, JVM will virtually never outperform C++.
- dathinab 3y ago
  It's not a lie at all. That's why there is profile guided optimizations for C/C++. Which instruments you C/C++ code to collect that needed additional information (on the cost of performance). Then when recompiling you can feed that collected information into your system. The problem with profile guided optimization is that it's way more annoying to deploy as on every update you have to deploy it twice once slower then naive and then once faster. And because the slower part might very well be to slow you might want to only deploy it to some nodes of a load balancer and deploy naive compiled versions to the other. It also means you have a similar slower => faster startup time, excepts it's of your program as whole instead of for each restart of a node. And while optimized Java likely will never outperform optimized C++ that is Java specific furthermore if we speak about common non manual optimized code which isn't implementing some tight math/CS algorithms (i.e. very common daily code in many companies) then the difference really isn't that big, small enough to make choosing java over C++ for server stuff a "in general" the right choice. (If you are not a company which only gets the "best" programmers like google). I mean just to put it into context there are companies which had success with stuff like running high speed trading code on the JVM and it was a success. So if you can do that probably Java doesn't have a major performance problem. > not over relying on RAII you mean like throwing out all the major improvements of C++ which majorly reduced the probability of non highly expert programmers introducing bugs which could be turned into RCEs?
  - wredue 3y ago
    Suggesting that you shouldn’t be allocating memory and then immediately tossing it doesn’t only suggest that you should practice RCE prone manual strategies. RAII is dogshit because it encourages and hides the fact of what’s really happening, leading to crazy performance gotchas. Just knowing the gotchas around it is often enough for any half way competent programmer to devise better code.
    - dathinab 3y ago
      RAII is the foundation of safe memory management in C++
- GeneralMayhem 3y ago
  If the "more information" is useless, it can be ignored. JIT can't possibly be a worse strategy, because a JIT always has the option of simply doing an AOT compile at program start. That doesn't mean that in practice the JVM is faster than well-written C++; the Java language semantics almost prevent it from doing so in the general case. But in principle, if all else were equal, it should be able to be.

wredue 3y ago

“Has more information therefor better optimized” is bordering on a lie, is the problem. Theres truth to a point I guess, but it’s also true that lots of “more information” is useless, and sometimes harmful to optimization, and additionally that it’s really diminishing returns. Truth is as long as you’re not over relying on RAII, JVM will virtually never outperform C++.

dathinab 3y ago
It's not a lie at all. That's why there is profile guided optimizations for C/C++. Which instruments you C/C++ code to collect that needed additional information (on the cost of performance). Then when recompiling you can feed that collected information into your system. The problem with profile guided optimization is that it's way more annoying to deploy as on every update you have to deploy it twice once slower then naive and then once faster. And because the slower part might very well be to slow you might want to only deploy it to some nodes of a load balancer and deploy naive compiled versions to the other. It also means you have a similar slower => faster startup time, excepts it's of your program as whole instead of for each restart of a node. And while optimized Java likely will never outperform optimized C++ that is Java specific furthermore if we speak about common non manual optimized code which isn't implementing some tight math/CS algorithms (i.e. very common daily code in many companies) then the difference really isn't that big, small enough to make choosing java over C++ for server stuff a "in general" the right choice. (If you are not a company which only gets the "best" programmers like google). I mean just to put it into context there are companies which had success with stuff like running high speed trading code on the JVM and it was a success. So if you can do that probably Java doesn't have a major performance problem. > not over relying on RAII you mean like throwing out all the major improvements of C++ which majorly reduced the probability of non highly expert programmers introducing bugs which could be turned into RCEs?
- wredue 3y ago
  Suggesting that you shouldn’t be allocating memory and then immediately tossing it doesn’t only suggest that you should practice RCE prone manual strategies. RAII is dogshit because it encourages and hides the fact of what’s really happening, leading to crazy performance gotchas. Just knowing the gotchas around it is often enough for any half way competent programmer to devise better code.
  - dathinab 3y ago
    RAII is the foundation of safe memory management in C++
GeneralMayhem 3y ago
If the "more information" is useless, it can be ignored. JIT can't possibly be a worse strategy, because a JIT always has the option of simply doing an AOT compile at program start. That doesn't mean that in practice the JVM is faster than well-written C++; the Java language semantics almost prevent it from doing so in the general case. But in principle, if all else were equal, it should be able to be.