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