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Use HR-timers (when available) to deliver an accurate preemption tick. The regular scheduler tick that runs at 1/HZ can be too coarse when nice level are used. The fairness system will still keep the cpu utilisation 'fair' by then delaying the task that got an excessive amount of CPU time but try to minimize this by delivering preemption points spot-on. The average frequency of this extra interrupt is sched_latency / nr_latency. Which need not be higher than 1/HZ, its just that the distribution within the sched_latency period is important. Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Signed-off-by: Ingo Molnar <mingo@elte.hu>
59 lines
1.6 KiB
Plaintext
59 lines
1.6 KiB
Plaintext
#
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# Timer Interrupt Frequency Configuration
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#
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choice
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prompt "Timer frequency"
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default HZ_250
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help
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Allows the configuration of the timer frequency. It is customary
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to have the timer interrupt run at 1000 Hz but 100 Hz may be more
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beneficial for servers and NUMA systems that do not need to have
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a fast response for user interaction and that may experience bus
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contention and cacheline bounces as a result of timer interrupts.
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Note that the timer interrupt occurs on each processor in an SMP
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environment leading to NR_CPUS * HZ number of timer interrupts
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per second.
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config HZ_100
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bool "100 HZ"
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help
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100 Hz is a typical choice for servers, SMP and NUMA systems
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with lots of processors that may show reduced performance if
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too many timer interrupts are occurring.
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config HZ_250
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bool "250 HZ"
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help
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250 Hz is a good compromise choice allowing server performance
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while also showing good interactive responsiveness even
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on SMP and NUMA systems. If you are going to be using NTSC video
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or multimedia, selected 300Hz instead.
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config HZ_300
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bool "300 HZ"
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help
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300 Hz is a good compromise choice allowing server performance
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while also showing good interactive responsiveness even
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on SMP and NUMA systems and exactly dividing by both PAL and
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NTSC frame rates for video and multimedia work.
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config HZ_1000
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bool "1000 HZ"
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help
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1000 Hz is the preferred choice for desktop systems and other
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systems requiring fast interactive responses to events.
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endchoice
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config HZ
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int
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default 100 if HZ_100
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default 250 if HZ_250
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default 300 if HZ_300
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default 1000 if HZ_1000
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config SCHED_HRTICK
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def_bool HIGH_RES_TIMERS && X86
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