3.2. 解释硬件和固件延迟测试结果

例子

• 以下结果代表了经过调优的系统，可最小化固件系统中断。在这种情况下，hwlatdetect 的输出如下所示：

  # hwlatdetect --duration=60s
  hwlatdetect:  test duration 60 seconds
  	detector: tracer
  	parameters:
  		Latency threshold: 10us
  		Sample window:     1000000us
  		Sample width:      500000us
  		Non-sampling period:  500000us
  		Output File:       None
  
  Starting test
  test finished
  Max Latency: Below threshold
  Samples recorded: 0
  Samples exceeding threshold: 0

  Copy to Clipboard Toggle word wrap

• 以下结果代表了一个无法调整的系统，以便最大程度降低固件系统中断。在这种情况下，hwlatdetect 的输出如下所示：

  # hwlatdetect --duration=10s
  hwlatdetect:  test duration 10 seconds
  	detector: tracer
  	parameters:
  		Latency threshold: 10us
  		Sample window:     1000000us
  		Sample width:      500000us
  		Non-sampling period:  500000us
  		Output File:       None
  
  Starting test
  test finished
  Max Latency: 18us
  Samples recorded: 10
  Samples exceeding threshold: 10
  SMIs during run: 0
  ts: 1519674281.220664736, inner:17, outer:15
  ts: 1519674282.721666674, inner:18, outer:17
  ts: 1519674283.722667966, inner:16, outer:17
  ts: 1519674284.723669259, inner:17, outer:18
  ts: 1519674285.724670551, inner:16, outer:17
  ts: 1519674286.725671843, inner:17, outer:17
  ts: 1519674287.726673136, inner:17, outer:16
  ts: 1519674288.727674428, inner:16, outer:18
  ts: 1519674289.728675721, inner:17, outer:17
  ts: 1519674290.729677013, inner:18, outer:17----

  Copy to Clipboard Toggle word wrap

  这个结果显示，在连续读取系统时钟源时，会在 15-18 us 范围内显示 10 延迟。

  hwlatdetect 使用 tracer 机制来检测无法解释的延迟。

  注意

  之前的版本使用了内核模块而不是 ftrace tracer。