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