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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 # Timekeeping vsyscall support
 16 config GENERIC_TIME_VSYSCALL
 17         bool
 18 
 19 # Timekeeping vsyscall support
 20 config GENERIC_TIME_VSYSCALL_OLD
 21         bool
 22 
 23 # ktime_t scalar 64bit nsec representation
 24 config KTIME_SCALAR
 25         bool
 26 
 27 # Old style timekeeping
 28 config ARCH_USES_GETTIMEOFFSET
 29         bool
 30 
 31 # The generic clock events infrastructure
 32 config GENERIC_CLOCKEVENTS
 33         bool
 34 
 35 # Migration helper. Builds, but does not invoke
 36 config GENERIC_CLOCKEVENTS_BUILD
 37         bool
 38         default y
 39         depends on GENERIC_CLOCKEVENTS
 40 
 41 # Architecture can handle broadcast in a driver-agnostic way
 42 config ARCH_HAS_TICK_BROADCAST
 43         bool
 44 
 45 # Clockevents broadcasting infrastructure
 46 config GENERIC_CLOCKEVENTS_BROADCAST
 47         bool
 48         depends on GENERIC_CLOCKEVENTS
 49 
 50 # Automatically adjust the min. reprogramming time for
 51 # clock event device
 52 config GENERIC_CLOCKEVENTS_MIN_ADJUST
 53         bool
 54 
 55 # Generic update of CMOS clock
 56 config GENERIC_CMOS_UPDATE
 57         bool
 58 
 59 if GENERIC_CLOCKEVENTS
 60 menu "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.
 65 config TICK_ONESHOT
 66         bool
 67 
 68 config NO_HZ_COMMON
 69         bool
 70         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 71         select TICK_ONESHOT
 72 
 73 choice
 74         prompt "Timer tick handling"
 75         default NO_HZ_IDLE if NO_HZ
 76 
 77 config 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 
 83 config 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 
 94 config 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 
124 endchoice
125 
126 config 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 
136 config 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 
159 config 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 
186 config 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 
194 config 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 
203 endmenu
204 endif

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