jit

问题 The documentation seems to be wrong. Could someone tell me which is true? In Performance Myths section is: On devices without a JIT, caching field accesses is about 20% faster than repeatedly accesssing the field. With a JIT, field access costs about the same as local access. In Avoid Internal Getters/Setters section is: Without a JIT, direct field access is about 3x faster than invoking a trivial getter. With the JIT (where direct field access is as cheap as accessing a local), direct field

问题 "Consider a typical Windows x86 or AMD64 architecture, the memory is divided in executable sections that cannot be written to and data sections that can be written to but cannot be executed (think DEP)." "JIT compiles methods in-memory, does (generally) not store anything to disk, instead moves it around where the next instruction pointer can reach it, changes the current instruction pointer (pointing to the JIT) to point to the newly generated code and then executes it." These two paragraphs

问题 I recently read a discussion regarding whether managed languages are slower (or faster) than native languages (specifically C# vs C++). One person that contributed to the discussion said that the JIT compilers of managed languages would be able to make optimizations regarding references that simply isn't possible in languages that use pointers. What I'd like to know is what kind of optimizations that are possible on references and not on pointers? Note that the discussion was about execution

问题 A while back I provided an answer to this question. Objective: count the number of values in this matrix that are in the [3 6] range: A = [2 3 4 5 6 7; 7 6 5 4 3 2] I came up with 12 different ways to do it: count = numel(A( A(:)>3 & A(:)<6 )) %# (1) count = length(A( A(:)>3 & A(:)<6 )) %# (2) count = nnz( A(:)>3 & A(:)<6 ) %# (3) count = sum( A(:)>3 & A(:)<6 ) %# (4) Ac = A(:); count = numel(A( Ac>3 & Ac<6 )) %# (5,6,7,8) %# prevents double expansion %# similar for length(), nnz(), sum(), %#

问题 I am trying to understand how I can configure the type of JIT I want to use. Say, I am aware that there are 3 types of JIT (Pre, Econo and Normal). But have the following curious questions. What is the default JIT with which .NET runs in deployment server? Do we have the flexibility to change the settings to use either pre or econo if the default is normal. If so where I can change this? Not sure, if this setting is in machine.config or something? 回答1: I never heard of "Econo jit" before. I

问题 I'm trying to know whether creating a Class Data Sharing archive (by running java -Xshare:dump ) compiles byte code into native code. There is not a lot of documentation about the internals of Class Data Sharing. The page I linked says that java -Xshare:dump loads a set of classes from the system jar file into a private internal representation, and dumps that representation to a file. But says nothing about whether this code is compiled or not. (Possibly related: Speed up application start by

问题 The kernel provides a number of examples in samples/bpf . I am interested in building one of examples outside of the tree, just like we build a kernel module, where Makefile can be simple enough. Is it possible to do the same with bpf? I tried it by ripping out unnecessary parts from samples/bpf/Makefile and keeping dependencies to libbpf and others, however it turned out to be not that easy. For example, trying to build samples/bpf/bpf_tcp_kern.c outside of the kernel tree, with the

问题 What unusual, unexpected consequences have occurred in terms of performance, memory, etc when switching from running your .NET applications under the 64 bit JIT vs. the 32 bit JIT? I'm interested in the good, but more interested in the surprisingly bad issues people have run into. I am in the process of writing a new .NET application which will be deployed in both 32bit and 64bit. There have been many questions relating to the issues with porting the application - I am unconcerned with the

问题 In a lecture about JIT in Hotspot I want to give as many examples as possible of the specific optimizations that JIT performs. I know just about "method inlining", but there should be much more. Give a vote for every example. 回答1: Well, you should scan Brian Goetz's articles for examples. In brief, HotSpot can and will: Inline methods Join adjacent synchronized blocks on the same object Eliminate locks if monitor is not reachable from other threads Eliminate dead code (hence most of micro

问题 What are the advantages and disadvantages of pre-jitting assemblies in .NET? I heard that pre-jitting will improve performance. When should I pre-jit and when shouldn't I pre-jit? 回答1: "Pre-jitting" or pre-compiling will improve performance, at start up , because you would be skipping that step. The reason that .NET JITs every time an app and its libraries load is so that it can run on many platforms and architectures with the best possible optimizations without the need for managing your