The apache benchmark tool is very basic, and while it will give you a solid idea of some performance, it is a bad idea to only depend on it if you plan to have your site exposed to serious stress in production. Having said that, here’s the most common and simplest parameters: -c: (“Concurrency”). Indicates … Read more
CLOCKS_PER_SEC is a constant which is declared in <time.h>. To get the CPU time used by a task within a C application, use: clock_t begin = clock(); /* here, do your time-consuming job */ clock_t end = clock(); double time_spent = (double)(end – begin) / CLOCKS_PER_SEC; Note that this returns the time as a floating … Read more
There is no strict reason why a bytecode based language like C# or Java that has a JIT cannot be as fast as C++ code. However C++ code used to be significantly faster for a long time, and also today still is in many cases. This is mainly due to the more advanced JIT optimizations … Read more
There is a slight difference in the ordering of the bytecode. 2 * (i * i): iconst_2 iload0 iload0 imul imul iadd vs 2 * i * i: iconst_2 iload0 imul iload0 imul iadd At first sight this should not make a difference; if anything the second version is more optimal since it uses one … Read more
Inside a function, the bytecode is: 2 0 SETUP_LOOP 20 (to 23) 3 LOAD_GLOBAL 0 (xrange) 6 LOAD_CONST 3 (100000000) 9 CALL_FUNCTION 1 12 GET_ITER >> 13 FOR_ITER 6 (to 22) 16 STORE_FAST 0 (i) 3 19 JUMP_ABSOLUTE 13 >> 22 POP_BLOCK >> 23 LOAD_CONST 0 (None) 26 RETURN_VALUE At the top level, the bytecode … Read more
Tips about writing micro benchmarks from the creators of Java HotSpot: Rule 0: Read a reputable paper on JVMs and micro-benchmarking. A good one is Brian Goetz, 2005. Do not expect too much from micro-benchmarks; they measure only a limited range of JVM performance characteristics. Rule 1: Always include a warmup phase which runs your … Read more
tl;dr: Because of different default settings in C++ requiring more system calls. By default, cin is synchronized with stdio, which causes it to avoid any input buffering. If you add this to the top of your main, you should see much better performance: std::ios_base::sync_with_stdio(false); Normally, when an input stream is buffered, instead of reading one … Read more
Real, User and Sys process time statistics One of these things is not like the other. Real refers to actual elapsed time; User and Sys refer to CPU time used only by the process. Real is wall clock time – time from start to finish of the call. This is all elapsed time including time … Read more