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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 # Architecture can handle broadcast in a driver-agnostic way
 37 config ARCH_HAS_TICK_BROADCAST
 38         bool
 39 
 40 # Clockevents broadcasting infrastructure
 41 config GENERIC_CLOCKEVENTS_BROADCAST
 42         bool
 43         depends on GENERIC_CLOCKEVENTS
 44 
 45 # Automatically adjust the min. reprogramming time for
 46 # clock event device
 47 config GENERIC_CLOCKEVENTS_MIN_ADJUST
 48         bool
 49 
 50 # Generic update of CMOS clock
 51 config GENERIC_CMOS_UPDATE
 52         bool
 53 
 54 if GENERIC_CLOCKEVENTS
 55 menu "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.
 60 config TICK_ONESHOT
 61         bool
 62 
 63 config NO_HZ_COMMON
 64         bool
 65         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
 66         select TICK_ONESHOT
 67 
 68 choice
 69         prompt "Timer tick handling"
 70         default NO_HZ_IDLE if NO_HZ
 71 
 72 config 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 
 78 config 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 
 89 config 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         depends on HAVE_CONTEXT_TRACKING
 96         # VIRT_CPU_ACCOUNTING_GEN dependency
 97         depends on HAVE_VIRT_CPU_ACCOUNTING_GEN
 98         select NO_HZ_COMMON
 99         select RCU_NOCB_CPU
100         select VIRT_CPU_ACCOUNTING_GEN
101         select IRQ_WORK
102         help
103          Adaptively try to shutdown the tick whenever possible, even when
104          the CPU is running tasks. Typically this requires running a single
105          task on the CPU. Chances for running tickless are maximized when
106          the task mostly runs in userspace and has few kernel activity.
107 
108          You need to fill up the nohz_full boot parameter with the
109          desired range of dynticks CPUs.
110 
111          This is implemented at the expense of some overhead in user <-> kernel
112          transitions: syscalls, exceptions and interrupts. Even when it's
113          dynamically off.
114 
115          Say N.
116 
117 endchoice
118 
119 config NO_HZ_FULL_ALL
120        bool "Full dynticks system on all CPUs by default (except CPU 0)"
121        depends on NO_HZ_FULL
122        help
123          If the user doesn't pass the nohz_full boot option to
124          define the range of full dynticks CPUs, consider that all
125          CPUs in the system are full dynticks by default.
126          Note the boot CPU will still be kept outside the range to
127          handle the timekeeping duty.
128 
129 config NO_HZ_FULL_SYSIDLE
130         bool "Detect full-system idle state for full dynticks system"
131         depends on NO_HZ_FULL
132         default n
133         help
134          At least one CPU must keep the scheduling-clock tick running for
135          timekeeping purposes whenever there is a non-idle CPU, where
136          "non-idle" also includes dynticks CPUs as long as they are
137          running non-idle tasks.  Because the underlying adaptive-tick
138          support cannot distinguish between all CPUs being idle and
139          all CPUs each running a single task in dynticks mode, the
140          underlying support simply ensures that there is always a CPU
141          handling the scheduling-clock tick, whether or not all CPUs
142          are idle.  This Kconfig option enables scalable detection of
143          the all-CPUs-idle state, thus allowing the scheduling-clock
144          tick to be disabled when all CPUs are idle.  Note that scalable
145          detection of the all-CPUs-idle state means that larger systems
146          will be slower to declare the all-CPUs-idle state.
147 
148          Say Y if you would like to help debug all-CPUs-idle detection.
149 
150          Say N if you are unsure.
151 
152 config NO_HZ_FULL_SYSIDLE_SMALL
153         int "Number of CPUs above which large-system approach is used"
154         depends on NO_HZ_FULL_SYSIDLE
155         range 1 NR_CPUS
156         default 8
157         help
158          The full-system idle detection mechanism takes a lazy approach
159          on large systems, as is required to attain decent scalability.
160          However, on smaller systems, scalability is not anywhere near as
161          large a concern as is energy efficiency.  The sysidle subsystem
162          therefore uses a fast but non-scalable algorithm for small
163          systems and a lazier but scalable algorithm for large systems.
164          This Kconfig parameter defines the number of CPUs in the largest
165          system that will be considered to be "small".
166 
167          The default value will be fine in most cases.  Battery-powered
168          systems that (1) enable NO_HZ_FULL_SYSIDLE, (2) have larger
169          numbers of CPUs, and (3) are suffering from battery-lifetime
170          problems due to long sysidle latencies might wish to experiment
171          with larger values for this Kconfig parameter.  On the other
172          hand, they might be even better served by disabling NO_HZ_FULL
173          entirely, given that NO_HZ_FULL is intended for HPC and
174          real-time workloads that at present do not tend to be run on
175          battery-powered systems.
176 
177          Take the default if you are unsure.
178 
179 config NO_HZ
180         bool "Old Idle dynticks config"
181         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
182         help
183           This is the old config entry that enables dynticks idle.
184           We keep it around for a little while to enforce backward
185           compatibility with older config files.
186 
187 config HIGH_RES_TIMERS
188         bool "High Resolution Timer Support"
189         depends on !ARCH_USES_GETTIMEOFFSET && GENERIC_CLOCKEVENTS
190         select TICK_ONESHOT
191         help
192           This option enables high resolution timer support. If your
193           hardware is not capable then this option only increases
194           the size of the kernel image.
195 
196 endmenu
197 endif

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