编译:gcc -O2 unlikely.cpp -o unlikely 反汇编一下,看看汇编:objdump -S unlikely 108048380:28048380:55push%ebp38048381:89e5mov%esp,%ebp48048383:83e4 f0and$0xfffffff0,%esp58048386:83ec10sub$0x10,%esp68048389: 8b450cmov0xc(%ebp),%eax7804838c: c74424080a0000movl $0xa,0x8(%esp)88048393:009804...
yswenli 20 26906 c/c++概述 2019-12-09 17:17 − c/c++的学习分为两个部分一、语言标准语言标准定义了功能特性和标准库两部分。功能特性由编译器负责具体实现,比如linux下gcc,windows下Visual Studio 标准库实现依赖于具体平台,比如linux下c标准库是glibc,windows下的MSVCRT.DLL。 c/c++是... 翟云云 0...
#define likely(x) __builtin_expect(!!(x), 1) //gcc内置函数, 帮助编译器分支优化 #define unlikely(x) __builtin_expect(!!(x), 0) if(likely(condition)) { // 这里的代码执行的概率比较高 } if(unlikely(condition)) { // 这里的代码执行的概率比较高 } // 尽量避免远调用 1. 2. 3. ...
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if (unlikely(latency_req == 0)) return 0; /* determine the expected residency time, round up */ t = ktime_to_timespec(tick_nohz_get_sleep_length()); data->expected_us = t.tv_sec * USEC_PER_SEC + t.tv_nsec / NSEC_PER_USEC; ...
(unlikely(latency_req==0))return0;/* determine the expected residency time, round up */t=ktime_to_timespec(tick_nohz_get_sleep_length());data->expected_us=t.tv_sec*USEC_PER_SEC+t.tv_nsec/NSEC_PER_USEC;data->bucket=which_bucket(data->expected_us);multiplier=performance_multiplier();...
我穿插一句补充,由于代码出现了分支,于是不管两路分支出现的概率如何,程序永远不可能同时走两路,因此代码的利用率就被降低了,就像修了两条路,但是你永远只能走一条。最糟糕的情况是,利用率只有50%。当然关于两路分支的概率的话题,有机会再来探讨内核中的 likely 和 unlikely 的详细内幕。
it aborts with the invalid parameter handler. If you need truncation behavior, be sure to use strncpy_s with _TRUNCATE. In general, truncation is unlikely to be the right choice unless your code is producing user-interface or other non-system output. Truncating file paths, for example, can ...