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# Clocksources require validation of the clocksource against the last 16# cycle update - x86/TSC misfeature 17config CLOCKSOURCE_VALIDATE_LAST_CYCLE 18 bool 19 20# Timekeeping vsyscall support 21config GENERIC_TIME_VSYSCALL 22 bool 23 24# Timekeeping vsyscall support 25config GENERIC_TIME_VSYSCALL_OLD 26 bool 27 28# Old style timekeeping 29config ARCH_USES_GETTIMEOFFSET 30 bool 31 32# The generic clock events infrastructure 33config GENERIC_CLOCKEVENTS 34 bool 35 36# Migration helper. Builds, but does not invoke 37config GENERIC_CLOCKEVENTS_BUILD 38 bool 39 default y 40 depends on GENERIC_CLOCKEVENTS 41 42# Architecture can handle broadcast in a driver-agnostic way 43config ARCH_HAS_TICK_BROADCAST 44 bool 45 46# Clockevents broadcasting infrastructure 47config GENERIC_CLOCKEVENTS_BROADCAST 48 bool 49 depends on GENERIC_CLOCKEVENTS 50 51# Automatically adjust the min. reprogramming time for 52# clock event device 53config GENERIC_CLOCKEVENTS_MIN_ADJUST 54 bool 55 56# Generic update of CMOS clock 57config GENERIC_CMOS_UPDATE 58 bool 59 60if GENERIC_CLOCKEVENTS 61menu "Timers subsystem" 62 63# Core internal switch. Selected by NO_HZ_COMMON / HIGH_RES_TIMERS. This is 64# only related to the tick functionality. Oneshot clockevent devices 65# are supported independ of this. 66config TICK_ONESHOT 67 bool 68 69config NO_HZ_COMMON 70 bool 71 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 72 select TICK_ONESHOT 73 74choice 75 prompt "Timer tick handling" 76 default NO_HZ_IDLE if NO_HZ 77 78config HZ_PERIODIC 79 bool "Periodic timer ticks (constant rate, no dynticks)" 80 help 81 This option keeps the tick running periodically at a constant 82 rate, even when the CPU doesn't need it. 83 84config NO_HZ_IDLE 85 bool "Idle dynticks system (tickless idle)" 86 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 87 select NO_HZ_COMMON 88 help 89 This option enables a tickless idle system: timer interrupts 90 will only trigger on an as-needed basis when the system is idle. 91 This is usually interesting for energy saving. 92 93 Most of the time you want to say Y here. 94 95config NO_HZ_FULL 96 bool "Full dynticks system (tickless)" 97 # NO_HZ_COMMON dependency 98 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 99 # We need at least one periodic CPU for timekeeping 100 depends on SMP 101 # RCU_USER_QS dependency 102 depends on HAVE_CONTEXT_TRACKING 103 # VIRT_CPU_ACCOUNTING_GEN dependency 104 depends on HAVE_VIRT_CPU_ACCOUNTING_GEN 105 select NO_HZ_COMMON 106 select RCU_USER_QS 107 select RCU_NOCB_CPU 108 select VIRT_CPU_ACCOUNTING_GEN 109 select IRQ_WORK 110 help 111 Adaptively try to shutdown the tick whenever possible, even when 112 the CPU is running tasks. Typically this requires running a single 113 task on the CPU. Chances for running tickless are maximized when 114 the task mostly runs in userspace and has few kernel activity. 115 116 You need to fill up the nohz_full boot parameter with the 117 desired range of dynticks CPUs. 118 119 This is implemented at the expense of some overhead in user <-> kernel 120 transitions: syscalls, exceptions and interrupts. Even when it's 121 dynamically off. 122 123 Say N. 124 125endchoice 126 127config NO_HZ_FULL_ALL 128 bool "Full dynticks system on all CPUs by default (except CPU 0)" 129 depends on NO_HZ_FULL 130 help 131 If the user doesn't pass the nohz_full boot option to 132 define the range of full dynticks CPUs, consider that all 133 CPUs in the system are full dynticks by default. 134 Note the boot CPU will still be kept outside the range to 135 handle the timekeeping duty. 136 137config NO_HZ_FULL_SYSIDLE 138 bool "Detect full-system idle state for full dynticks system" 139 depends on NO_HZ_FULL 140 default n 141 help 142 At least one CPU must keep the scheduling-clock tick running for 143 timekeeping purposes whenever there is a non-idle CPU, where 144 "non-idle" also includes dynticks CPUs as long as they are 145 running non-idle tasks. Because the underlying adaptive-tick 146 support cannot distinguish between all CPUs being idle and 147 all CPUs each running a single task in dynticks mode, the 148 underlying support simply ensures that there is always a CPU 149 handling the scheduling-clock tick, whether or not all CPUs 150 are idle. This Kconfig option enables scalable detection of 151 the all-CPUs-idle state, thus allowing the scheduling-clock 152 tick to be disabled when all CPUs are idle. Note that scalable 153 detection of the all-CPUs-idle state means that larger systems 154 will be slower to declare the all-CPUs-idle state. 155 156 Say Y if you would like to help debug all-CPUs-idle detection. 157 158 Say N if you are unsure. 159 160config NO_HZ_FULL_SYSIDLE_SMALL 161 int "Number of CPUs above which large-system approach is used" 162 depends on NO_HZ_FULL_SYSIDLE 163 range 1 NR_CPUS 164 default 8 165 help 166 The full-system idle detection mechanism takes a lazy approach 167 on large systems, as is required to attain decent scalability. 168 However, on smaller systems, scalability is not anywhere near as 169 large a concern as is energy efficiency. The sysidle subsystem 170 therefore uses a fast but non-scalable algorithm for small 171 systems and a lazier but scalable algorithm for large systems. 172 This Kconfig parameter defines the number of CPUs in the largest 173 system that will be considered to be "small". 174 175 The default value will be fine in most cases. Battery-powered 176 systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger 177 numbers of CPUs, and (3) are suffering from battery-lifetime 178 problems due to long sysidle latencies might wish to experiment 179 with larger values for this Kconfig parameter. On the other 180 hand, they might be even better served by disabling NO_HZ_FULL 181 entirely, given that NO_HZ_FULL is intended for HPC and 182 real-time workloads that at present do not tend to be run on 183 battery-powered systems. 184 185 Take the default if you are unsure. 186 187config NO_HZ 188 bool "Old Idle dynticks config" 189 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 190 help 191 This is the old config entry that enables dynticks idle. 192 We keep it around for a little while to enforce backward 193 compatibility with older config files. 194 195config HIGH_RES_TIMERS 196 bool "High Resolution Timer Support" 197 depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS 198 select TICK_ONESHOT 199 help 200 This option enables high resolution timer support. If your 201 hardware is not capable then this option only increases 202 the size of the kernel image. 203 204endmenu 205endif 206