Timer Frequency
Yamaken
Status: New User - Welcome
Joined: 19 Aug 2019
Posts: 1
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Hi! I have installed this kernel in my dedicated server(stated by the "Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 5.2.0-9.1-liquorix-amd64 x86_64)" after ssh login) and i have run this command to know the timer frequency: "grep 'CONFIG_HZ' /boot/config-5.2.0-9.1-liquorix-amd64" and the results are:


:: Quote ::
CONFIG_HZ_PERIODIC=y
# CONFIG_HZ_100 is not set
CONFIG_HZ_250=y
# CONFIG_HZ_300 is not set
# CONFIG_HZ_1000 is not set
CONFIG_HZ=250


I have read here([link]) that this kernel had it set to 1000 mhz. Is the output of the command correct?
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damentz
Status: Assistant
Joined: 09 Sep 2008
Posts: 760
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Why Liquorix is set to a periodic timer of 250hz is a long story.

Ideally, I would prefer running 1000hz with tickless idle, but MuQSS exhibits unusual timekeeping behavior that has unwanted side-effects. The two most noticeable side-effects are:

1) CPU usage in top and other related tools doesn't seem quite right when idle.
2) CPU frequency governors don't have enough information to know they can ramp down the frequency, thus without information about the CPU being idle, the governors always thing the CPU is busy, thus ramping the frequency up.

To fix this, I had to run Liquorix on a periodic timer instead of tickless idle. This had another huge side-effect, old systems would generate coil whine from the high tick frequency. Modern laptops would idle very badly and pull far more power than necessary while doing nothing.

The compromise is running 250hz periodic. This gives the CPU governors ondemand and intel-pstate enough information at a regular basis to downclock the CPU when idle, and the reduce tick frequency lets Intel CPUs idle in their C6/C7 states more efficiently, drastically reducing power usage.

I've tried 100hz but time accounting seems broken there as well, so 250hz is as coarse as I'm willing to go. Fortunately, MuQSS completely sidesteps the poor time accounting with high resolution timers (currently set at 2ms granularity), so for the most part, most problems with low tick frequency have been mitigated.

Hopefully that explains what happened and why Liquorix is configured so differently than most distributions stock kernel and linux-zen itself.
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