日期：2016年3月1日

Profiling CPU使用

本文内容取自于《Systems Performance: Enterprise and the Cloud》。

Profiling CPU的方法是通过对CPU状态进行周期性地采样，然后进行分析。包含5个步骤：

1. Select the type of profile data to capture, and the rate.
2. Begin sampling at a timed interval.
3. Wait while the activity of interest occurs.
4. End sampling and collect sample data.
5. Process the data.

CPU采样数据基于下面两个因素：

a. User level, kernel level, or both
b. Function and offset (program-counter-based), function only, partial stack trace, or full stack trace

抓取user level和kernel level所有的函数调用栈固然可以完整地得到CPU的profile，但这样会产生太多的数据。因此通常只采样user level或kernel level部分函数调用栈就可以了，有时可能仅需要保留函数的名字。

下面是一个使用DTrace对CPU采样的例子：

 # dtrace -qn 'profile-997 /arg1/ {@[execname, ufunc(arg1)] = count();} tick-10s{exit(0)}'

 top                                                 libc.so.7`0x801154fec                                             1
 top                                                 libc.so.7`0x8011e5f28                                             1
 top                                                 libc.so.7`0x8011f18a9                                             1

 

Go语言的类型转换

以下摘自The Go Programming Language：

For every type T, there is a corresponding conversion operation T(x) that converts the value x to type T. A conversion from one type to another is allowed if both have the same underlying type, or if both are unnamed pointer types that point to variables of the same underlying type; these conversions change the type but not the representation of the value. If x is assignable to T, a conversion is permitted but is usually redundant.

Conversions are also allowed between numeric types, and between string and some slice types. These conversions may change the representation of the value. For instance, converting a floating-point number to an integer discards any fractional part, and converting a string to a []byte slice allocates a copy of the string data. In any case, a conversion never fails at run time.