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Linux/kernel/time/Kconfig

  1 #
  2 # Timer subsystem related configuration options
  3 #
  4 
  5 # Options selectable by arch Kconfig
  6 
  7 # Watchdog function for clocksources to detect instabilities
  8 config CLOCKSOURCE_WATCHDOG
  9         bool
 10 
 11 # Architecture has extra clocksource data
 12 config ARCH_CLOCKSOURCE_DATA
 13         bool
 14 
 15 # Clocksources require validation of the clocksource against the last
 16 # cycle update - x86/TSC misfeature
 17 config CLOCKSOURCE_VALIDATE_LAST_CYCLE
 18         bool
 19 
 20 # Timekeeping vsyscall support
 21 config GENERIC_TIME_VSYSCALL
 22         bool
 23 
 24 # Timekeeping vsyscall support
 25 config GENERIC_TIME_VSYSCALL_OLD
 26         bool
 27 
 28 # Old style timekeeping
 29 config ARCH_USES_GETTIMEOFFSET
 30         bool
 31 
 32 # The generic clock events infrastructure
 33 config GENERIC_CLOCKEVENTS
 34         bool
 35 
 36 # Migration helper. Builds, but does not invoke
 37 config GENERIC_CLOCKEVENTS_BUILD
 38         bool
 39         default y
 40         depends on GENERIC_CLOCKEVENTS
 41 
 42 # Architecture can handle broadcast in a driver-agnostic way
 43 config ARCH_HAS_TICK_BROADCAST
 44         bool
 45 
 46 # Clockevents broadcasting infrastructure
 47 config GENERIC_CLOCKEVENTS_BROADCAST
 48         bool
 49         depends on GENERIC_CLOCKEVENTS
 50 
 51 # Automatically adjust the min. reprogramming time for
 52 # clock event device
 53 config GENERIC_CLOCKEVENTS_MIN_ADJUST
 54         bool
 55 
 56 # Generic update of CMOS clock
 57 config GENERIC_CMOS_UPDATE
 58         bool
 59 
 60 if GENERIC_CLOCKEVENTS
 61 menu "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.
 66 config TICK_ONESHOT
 67         bool
 68 
 69 config NO_HZ_COMMON
 70         bool
 71         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 72         select TICK_ONESHOT
 73 
 74 choice
 75         prompt "Timer tick handling"
 76         default NO_HZ_IDLE if NO_HZ
 77 
 78 config 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 
 84 config 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 
 95 config 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 
125 endchoice
126 
127 config 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 
137 config 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 
160 config 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 
187 config 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 
195 config 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 
204 endmenu
205 endif

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