Documentation/timers/highres.rst

2 High resolution timers and dynamic ticks design notes
8 https://www.kernel.org/doc/ols/2006/ols2006v1-pages-333-346.pdf
11 http://www.cs.columbia.edu/~nahum/w6998/papers/ols2006-hrtimers-slides.pdf
23 - hrtimer base infrastructure
24 - timeofday and clock source management
25 - clock event management
26 - high resolution timer functionality
27 - dynamic ticks
31 ---------------------------
34 the base implementation are covered in Documentation/timers/hrtimers.rst. See
38 timers are:
40        - time ordered enqueueing into a rb-tree
41        - independent of ticks (the processing is based on nanoseconds)
45 -------------------------------------
48 code out of the architecture-specific areas into a generic management
64 Timers" was written by J. Stultz, D.V. Hart, & N. Aravamudan.
70 ----------------------
81 to touch all the architecture-specific implementations in order to provide new
82 functionality like high resolution timers or dynamic ticks.
95 structure with clock-specific property parameters and callback functions. The
98 includes the distinction of per-CPU and per-system global event devices.
100 System-level global event devices are used for the Linux periodic tick. Per-CPU
101 event devices are used to provide local CPU functionality such as process
102 accounting, profiling, and high resolution timers.
107       - system global periodic tick (jiffies update)
108       - cpu local update_process_times
109       - cpu local profiling
110       - cpu local next event interrupt (non periodic mode)
134 enabling of high resolution timers and dynamic ticks is simply provided by
143 -----------------------------------
156 configured for high resolution timers can run on a system which lacks the
163 dynamic ticks on i386 SMP systems which stop the local APIC in C3 power
167 The time ordered insertion of timers provides all the infrastructure to decide
169 decision is made per timer base and synchronized across per-cpu timer bases in
170 a support function. The design allows the system to utilize separate per-CPU
171 clock event devices for the per-CPU timer bases, but currently only one
172 reprogrammable clock event device per-CPU is utilized.
175 from the clock event distribution code and moves expired timers from the
176 red-black tree to a separate double linked list and invokes the softirq
182 context is the avoidance of up to two context switches - from the interrupted
187 switched off. This disables the per system global periodic clock event device -
190 The periodic tick functionality is provided by an per-cpu hrtimer. The callback
202 timers. The execution of this softirq can still be delayed by other softirqs,
209 -------------
215 - hrtimer_stop_sched_tick
216 - hrtimer_restart_sched_tick
217 - hrtimer_update_jiffies