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Events and the Kernel

news 来源：原创 2024/9/19 16:16:35

http://qnx.com/developers/docs/7.1/index.html#com.qnx.doc.sat/topic/events.html

qnx 内核产生内核事件

kernel calls
scheduling activity
interrupt handling
thread/process creation, destruction, and state changes

In addition, the instrumented kernel also inserts “artificial” events for:

time events
user events that may be used as “marker flags

Kernel Buffer Management

Each buffer is of a fixed size and is divided into a fixed number of slots:

Event buffer slots per buffer: 1024
Event buffer slot size: 16 bytes
Buffer size: 16 KB

简单的内核事件一个slot 够了，组合复杂事件需要多个slot 保存

当一个buffer 满了，proc-to 就会发生_NTO_HOOK_TRACE synthetic interrupt通知data-capture 程序读准备好可以取数据

To ensure this never happens, the instrumented kernel requests a buffer flush at the high-water mark.

The high-water mark is set at an efficient, yet conservative, level:

around 70% (_TRACEBUF_MAX_EVENTS) for linear mode
around 95% (_TRACEBUF_MAX_EVENTS_RING) for ring mode

由于中断里不能保存buffer ，因此系统在buffer填充达到一个水位就产生中断通知取数据

Capturing Trace Data

抓事件程序与内核交互，将内核发送事件保存到文件系统，抓取配置

buffer allocations (size)
which events and classes of events to log (filtering)
whether to log the events in wide mode or fast mode

抓取程序：

You can control the capture of data via qconn (under the control of the IDE), tracelogger (from the command line), or directly from your application. All three approaches use the TraceEvent() function to control the instrumented kernel:

tracelogger 抓取模式

Mode	Option	The kernel:	tracelogger:
Continuous	-c	Logs events	Captures the events, and continues to do so until terminated
Daemon	-d1	Doesn't log eventsa	Waits passivelya
Iterations (the default)	-n	Logs events	Captures num_buffers of data and then terminates
Ring	-r	Logs events	Doesn't capture events until it gets a SIGINT signal, or an application calls TraceEvent()b with a command of _NTO_TRACE_STOP
Time-based	-s	Logs events	Captures events for the specified number of seconds

By default, the instrumented kernel and tracelogger collect data in fast mode; to switch to wide mode, specify the -w option when you start tracelogger

By default, tracelogger captures all events from all classes, but you can disable the tracing of events from the classes as follows