The introduction of adaptive-ticks CPUs (Dynamic ticks) in UEK R4 represent a significant step forward on getting rid of the timer tick/interrupt (Full tickless operation).
“That interrupt is the CPU’s cue to reconsider which process should be running, catch up with read-copy-update (RCU) callbacks, and generally handle any necessary housekeeping.” Ref
This periodic timer interpret “interference” (based on CONFIG_HZ) have an effect on performance and power consumption which makes developers wish to abolish it. In previous version, a partial solution was used that consist on disabling timer tick for idle CPU which is controlled by the configuration option CONFIG_NO_HZ.This mode reduced considerably the power usage as it allowed idle CPU to stay in deeper c-state. What adaptive ticks feature bring us is the possibility to reduce the timer interrupt to 1 tick/second (1HZ) for non idle CPU having only one runnable task. This feature minimizes kernel overhead (up to 1%) and the potential latency problem , it was primarily targeted for High-performance computing (HPC) and real time application so it’s not necessary for every one.
For more info on Nearly full tickless operation please check this articles as most of the information here come from there :
- http://lwn.net/Articles/549580/
- http://lwn.net/Articles/549592/
- https://www.kernel.org/doc/Documentation/timers/NO_HZ.txt
- http://www.breakage.org/2013/11/15/nohz_fullgodmode/
- https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/7/html/Performance_Tuning_Guide/sect-Red_Hat_Enterprise_Linux-Performance_Tuning_Guide-CPU-Configuration_suggestions.html
TIME TO TEST :
- ORACLE 12.1.0.2.6
- OEL : 4.1.12-32.1.2.el6uek.x86_64
- 4 CPU : 2 sockets / 2 cores per socket Continue reading
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