Documentation/timers/highres.rst

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 ---------------------------
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
70 ----------------------
74 interrupt(s). The next event is currently defined to be periodic, with its
76 for various event driven functionalities is hardwired into the architecture
79 event interrupt devices other than those already built into the
81 to touch all the architecture-specific implementations in order to provide new
86 event driven kernel functionalities. The goal of the clock event subsystem is
90 architectures as it provides generic functionality down to the interrupt
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
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)
112 The clock event device delegates the selection of those timer interrupt related
116 architecture specific timer interrupt handlers and hands the control over the
117 clock event devices and the assignment of timer interrupt related functionality
122 interrupt, clock event device notification service and support for suspend and
133 to the clock event device and timer interrupt code. After the conversion the
143 -----------------------------------
161 calls when an interrupt happens. The overhead would be much larger than the
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.
174 When the timer interrupt happens, the next event interrupt handler is called
176 red-black tree to a separate double linked list and invokes the softirq
178 execute callback functions directly from the next event interrupt handler. This
179 is restricted to code which can safely be executed in the hard interrupt
181 used by nanosleep. The advantage of executing the handler in the interrupt
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
191 function is executed in the next event interrupt context and updates jiffies
209 -------------
215 - hrtimer_stop_sched_tick
216 - hrtimer_restart_sched_tick
217 - hrtimer_update_jiffies
224 called when an interrupt happens during the idle period, which does not cause a
225 reschedule. The call is necessary as the interrupt handler might have armed a
233 hrtimer_update_jiffies() is called from irq_enter() when an interrupt happens
234 in the idle period to make sure that jiffies are up to date and the interrupt