I read the manual of perf list, and find the following PMU event definitions of memory load/store:
mem-loads OR cpu/mem-loads/ [Kernel PMU event]
mem-stores OR cpu/mem-stores/ [Kernel PMU event]
But I always read perf script which uses "cpu/mem-loads/pp" instead of "cpu/mem-loads/". What is the difference between them? Are they the same thing? I have tried to google the answers, but can't find the explanation.
The p modifier stands for precise level When doing sampling, it used to indicate the skid you tolerate: how far can be t reported instruction from the effective instructions that generated the sample. pp means that the SAMPLE_IP is requested to have 0 skid. In other word, when you do memory accesses sampling, you want to know exactly which instruction generated the access.
See 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
