“cpu/mem-loads/pp”和“cpu/mem-loads/”有什么区别？答案

【问题标题】：What is the difference between "cpu/mem-loads/pp" and "cpu/mem-loads/"?“cpu/mem-loads/pp”和“cpu/mem-loads/”有什么区别？
【发布时间】：2015-02-06 03:15:28
【问题描述】：

我看了perf list的手册，发现memory load/store的PMU事件定义如下：

mem-loads OR cpu/mem-loads/                        [Kernel PMU event]
mem-stores OR cpu/mem-stores/                      [Kernel PMU event]

但我总是阅读perf 脚本，它使用“cpu/mem-loads/pp”而不是“cpu/mem-loads/”。它们之间有什么区别？它们是一样的吗？我试图用谷歌搜索答案，但找不到解释。

【问题讨论】：

标签： linux performance perf

【解决方案1】：

p 修饰符代表precise level 在进行采样时，它用于指示您可以容忍的打滑：从生成样本的有效指令到报告指令的距离。 pp 表示请求 SAMPLE_IP 具有 0 滑行。换句话说，当你做内存访问采样时，你想知道究竟是哪条指令产生了访问。

见man perf list:

p - precise level
....
       The p modifier can be used for specifying how precise the instruction address should be. The p modifier can be specified multiple times:

           0 - SAMPLE_IP can have arbitrary skid
           1 - SAMPLE_IP must have constant skid
           2 - SAMPLE_IP requested to have 0 skid
           3 - SAMPLE_IP must have 0 skid

       For Intel systems precise event sampling is implemented with PEBS which supports up to precise-level 2.

       On AMD systems it is implemented using IBS (up to precise-level 2). The precise modifier works with event types 0x76 (cpu-cycles, CPU clocks not halted) and 0xC1 (micro-ops
       retired). Both events map to IBS execution sampling (IBS op) with the IBS Op Counter Control bit (IbsOpCntCtl) set respectively (see AMD64 Architecture Programmer’s Manual Volume
       2: System Programming, 13.3 Instruction-Based Sampling). Examples to use IBS:

           perf record -a -e cpu-cycles:p ...    # use ibs op counting cycles
           perf record -a -e r076:p ...          # same as -e cpu-cycles:p
           perf record -a -e r0C1:p ...          # use ibs op counting micro-ops

【讨论】：