1# 2# Timer subsystem related configuration options 3# 4 5# Options selectable by arch Kconfig 6 7# Watchdog function for clocksources to detect instabilities 8config CLOCKSOURCE_WATCHDOG 9 bool 10 11# Architecture has extra clocksource data 12config ARCH_CLOCKSOURCE_DATA 13 bool 14 15# Timekeeping vsyscall support 16config GENERIC_TIME_VSYSCALL 17 bool 18 19# Timekeeping vsyscall support 20config GENERIC_TIME_VSYSCALL_OLD 21 bool 22 23# ktime_t scalar 64bit nsec representation 24config KTIME_SCALAR 25 bool 26 27# Old style timekeeping 28config ARCH_USES_GETTIMEOFFSET 29 bool 30 31# The generic clock events infrastructure 32config GENERIC_CLOCKEVENTS 33 bool 34 35# Migration helper. Builds, but does not invoke 36config GENERIC_CLOCKEVENTS_BUILD 37 bool 38 default y 39 depends on GENERIC_CLOCKEVENTS 40 41# Architecture can handle broadcast in a driver-agnostic way 42config ARCH_HAS_TICK_BROADCAST 43 bool 44 45# Clockevents broadcasting infrastructure 46config GENERIC_CLOCKEVENTS_BROADCAST 47 bool 48 depends on GENERIC_CLOCKEVENTS 49 50# Automatically adjust the min. reprogramming time for 51# clock event device 52config GENERIC_CLOCKEVENTS_MIN_ADJUST 53 bool 54 55# Generic update of CMOS clock 56config GENERIC_CMOS_UPDATE 57 bool 58 59if GENERIC_CLOCKEVENTS 60menu "Timers subsystem" 61 62# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 63# only related to the tick functionality. Oneshot clockevent devices 64# are supported independ of this. 65config TICK_ONESHOT 66 bool 67 68config NO_HZ_COMMON 69 bool 70 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 71 select TICK_ONESHOT 72 73choice 74 prompt "Timer tick handling" 75 default NO_HZ_IDLE if NO_HZ 76 77config HZ_PERIODIC 78 bool "Periodic timer ticks (constant rate, no dynticks)" 79 help 80 This option keeps the tick running periodically at a constant 81 rate, even when the CPU doesn't need it. 82 83config NO_HZ_IDLE 84 bool "Idle dynticks system (tickless idle)" 85 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 86 select NO_HZ_COMMON 87 help 88 This option enables a tickless idle system: timer interrupts 89 will only trigger on an as-needed basis when the system is idle. 90 This is usually interesting for energy saving. 91 92 Most of the time you want to say Y here. 93 94config NO_HZ_FULL 95 bool "Full dynticks system (tickless)" 96 # NO_HZ_COMMON dependency 97 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 98 # We need at least one periodic CPU for timekeeping 99 depends on SMP 100 # RCU_USER_QS dependency 101 depends on HAVE_CONTEXT_TRACKING 102 # VIRT_CPU_ACCOUNTING_GEN dependency 103 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 104 select NO_HZ_COMMON 105 select RCU_USER_QS 106 select RCU_NOCB_CPU 107 select VIRT_CPU_ACCOUNTING_GEN 108 select IRQ_WORK 109 help 110 Adaptively try to shutdown the tick whenever possible, even when 111 the CPU is running tasks. Typically this requires running a single 112 task on the CPU. Chances for running tickless are maximized when 113 the task mostly runs in userspace and has few kernel activity. 114 115 You need to fill up the nohz_full boot parameter with the 116 desired range of dynticks CPUs. 117 118 This is implemented at the expense of some overhead in user <-> kernel 119 transitions: syscalls, exceptions and interrupts. Even when it's 120 dynamically off. 121 122 Say N. 123 124endchoice 125 126config NO_HZ_FULL_ALL 127 bool "Full dynticks system on all CPUs by default (except CPU 0)" 128 depends on NO_HZ_FULL 129 help 130 If the user doesn't pass the nohz_full boot option to 131 define the range of full dynticks CPUs, consider that all 132 CPUs in the system are full dynticks by default. 133 Note the boot CPU will still be kept outside the range to 134 handle the timekeeping duty. 135 136config NO_HZ_FULL_SYSIDLE 137 bool "Detect full-system idle state for full dynticks system" 138 depends on NO_HZ_FULL 139 default n 140 help 141 At least one CPU must keep the scheduling-clock tick running for 142 timekeeping purposes whenever there is a non-idle CPU, where 143 "non-idle" also includes dynticks CPUs as long as they are 144 running non-idle tasks. Because the underlying adaptive-tick 145 support cannot distinguish between all CPUs being idle and 146 all CPUs each running a single task in dynticks mode, the 147 underlying support simply ensures that there is always a CPU 148 handling the scheduling-clock tick, whether or not all CPUs 149 are idle. This Kconfig option enables scalable detection of 150 the all-CPUs-idle state, thus allowing the scheduling-clock 151 tick to be disabled when all CPUs are idle. Note that scalable 152 detection of the all-CPUs-idle state means that larger systems 153 will be slower to declare the all-CPUs-idle state. 154 155 Say Y if you would like to help debug all-CPUs-idle detection. 156 157 Say N if you are unsure. 158 159config NO_HZ_FULL_SYSIDLE_SMALL 160 int "Number of CPUs above which large-system approach is used" 161 depends on NO_HZ_FULL_SYSIDLE 162 range 1 NR_CPUS 163 default 8 164 help 165 The full-system idle detection mechanism takes a lazy approach 166 on large systems, as is required to attain decent scalability. 167 However, on smaller systems, scalability is not anywhere near as 168 large a concern as is energy efficiency. The sysidle subsystem 169 therefore uses a fast but non-scalable algorithm for small 170 systems and a lazier but scalable algorithm for large systems. 171 This Kconfig parameter defines the number of CPUs in the largest 172 system that will be considered to be "small". 173 174 The default value will be fine in most cases. Battery-powered 175 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger 176 numbers of CPUs, and (3) are suffering from battery-lifetime 177 problems due to long sysidle latencies might wish to experiment 178 with larger values for this Kconfig parameter. On the other 179 hand, they might be even better served by disabling NO_HZ_FULL 180 entirely, given that NO_HZ_FULL is intended for HPC and 181 real-time workloads that at present do not tend to be run on 182 battery-powered systems. 183 184 Take the default if you are unsure. 185 186config NO_HZ 187 bool "Old Idle dynticks config" 188 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 189 help 190 This is the old config entry that enables dynticks idle. 191 We keep it around for a little while to enforce backward 192 compatibility with older config files. 193 194config HIGH_RES_TIMERS 195 bool "High Resolution Timer Support" 196 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 197 select TICK_ONESHOT 198 help 199 This option enables high resolution timer support. If your 200 hardware is not capable then this option only increases 201 the size of the kernel image. 202 203endmenu 204endif 205