Shapers in Linux

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HZ or HRTICKS mode

  • Your kernel must have option CONFIG_HIGH_RES_TIMERS=y
  • Prefferable(or mandatory? not sure) also to have CONFIG_NO_HZ=y
  • If your kernel works in HRTICKS mode you will see: 
Switched to high resolution mode on CPU 0

In case of failure, you can see 

Could not switch to high resolution mode on CPU 0

If it is failed, you will run in HZ mode.

cat /proc/net/psched 

# cat /proc/net/psched
000003e8 00000400 000f4240 000003e8

0x3e8 - means 1/1000 sec resolution, not hrtick. 

Router-Dora ~ # cat /proc/net/psched
000003e8 00000400 000f4240 3b9aca00

Means 0x3b9aca00 = 1/1000000000 sec resolution. Hrtimer. Thats what we need!

  • In HZ mode - HZ matter. 100 HZ will have much worse precision than 1000 HZ.
  • In HRTICKS mode HZ PROBABLY matter. I'm still researching this.
  • With 100 Hz imprecision can be +-5%. 1000 Hz - around 1-0.5%
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