System Performance

性能之巅：洞悉系统、企业与云计算

1. Time Scale : 时间比例
2. Perspectives : 视角
3. Saturation : 饱和度。The degree to which more work is requested of a resource than it can process is saturation.Saturation begins to occur at 100% utilization (capacity-based), as extra work cannot be processed and begins to queue.
4. Drill-down analysis : 深入分析
5. Baseline statistics : 基线统计
6. Micro benchmarking : 微基准
7. Capacity planning : 容量规划
8. Observability tools : 可观测性工具
9. Performance Evaluation Activity : Analytical Modeling, Observability of a production system (Measurement), Experimental testing (Simulation)
10. Trap : 缺陷
11. When a function is called, the current set of CPU registers (which store the state of the CPU) is saved to the stack, and a new stack frame is added to the top for the current execution of the thread. Functions end execution by calling a 'return' CPU instruction, which removes the current stack and returns execution to the previous one, restoring its state.
12. The kernel also responds to service requests from devices. These are called interrupts, as they interrupt current execution.
13. LVM (Logical Volume Manager) : 逻辑卷
14. Profiling can determine which code paths are consuming CPU and for how long
15. flame graph : 火焰图
16. Stack Trace : 堆栈轨迹
17. sampling Java on-CPU stacks with DTrace jstack():

    dtrace -n 'profile-97 /pid == 1742/ { @[jstack(100)] = count(); }'

18. The number of software threads that are queued and ready to run is an important performance metric indicating CPU saturation.
19. CPI: Cycle Per Instruction metrics
20. stall cycle(停顿周期) while waiting on memory access
21. CPU 字长(Word Size) : 电脑技术中对CPU在单位时间内(同一时间)能一次处理的二进制数的位数叫字长。所以能处理字长为8位数据的CPU通常就叫8位的CPU。同理32位的CPU就能在单位时间内处理字长为32位的二进制数据。字节和字长的区别：由于常用的英文字符用8位二进制就可以表示，所以通常就将8位称为一个字节。字长的长度是不固定的，对于不同的CPU、字长的长度也不一样。8位的CPU一次只能处理一个字节，而32位的CPU一次就能处理4个字节，同理字长为64位的CPU一次可以处理8个字节。

References

1 理解Linux Load Average