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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         # 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 
119 endchoice
120 
121 config 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 
131 config 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 
154 config 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 
181 config 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 
189 config 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 
198 endmenu
199 endif

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