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What is clocksource in Linux?
The clocksource concept represents the generic API for clock sources management in the Linux kernel. Besides this, each architecture can provide a driver for the architecture-dependent real time clock, for example – CMOS/RTC – arch/x86/kernel/rtc. c for the x86 architecture.
What is clocksource?
Clocksource is a device that can give a timestamp whenever you need it. In other words, Clocksource is any ticking counter that allows you to get its value.
What is clocksource tsc?
15.1. Hardware Clocks. The preferred clock source is the Time Stamp Counter (TSC), but if it is not available the High Precision Event Timer (HPET) is the second best option. However, not all systems have HPET clocks and some HPET clocks can be unreliable.
What is KVM clock?
kvm-clock is a Linux clocksource like tsc and hpet. ( tsc is commonly used on physical machines.) The discussion at the URL below indicates that all clocksources act like time counters that are periodically read by interrupts.
What is external clock source?
The External Clock Oscillator mode allows the PIC® MCU to be run from an externally generated logic level signal and that signal used as the system clock source. When this mode is selected, the signal is fed into the OSC1 pin.
What is TSC frequency?
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset. The instruction RDTSC returns the TSC in EDX:EAX. In x86-64 mode, RDTSC also clears the upper 32 bits of RAX and RDX. Cyrix included a Time Stamp Counter in their MII.
What is Clock_monotonic_raw?
CLOCK_MONOTONIC_RAW (since Linux 2.6.28; Linux-specific) Similar to CLOCK_MONOTONIC, but provides access to a raw hardware-based time that is not subject to NTP adjustments or the incremental adjustments performed by adjtime(3). This clock does not count time that the system is suspended.
What is external clock?
The external frequency is the number of times per second this pulse cycles. For example, a motherboard with a pulse that cycles 100 million times per second has an external clock frequency of 100 megahertz.
What is a external oscillator?
External Clock Oscillator Mode. The External Clock Oscillator mode allows the PIC® MCU to be run from an externally generated logic level signal and that signal used as the system clock source. When this mode is selected, the signal is fed into the OSC1 pin.
What is TSC in CPU?
The Time Stamp Counter (TSC) is a 64-bit register present on all x86 processors since the Pentium. It counts the number of CPU cycles since its reset. Pentium competitors such as the Cyrix 6×86 did not always have a TSC and may consider RDTSC an illegal instruction.
What is invariant TSC?
The invariant TSC means that the TSC continues at a fixed rate regardless of the C-state or frequency of the processor (as long as the processor remains in the ACPI S0 state). This is indicated by the CPUID.80000007.EDX[8].
Is Java nanoTime monotonic?
nanoTime() is monotonic (if the underlying system supports it).
How to change the clock source in the system?
Overriding the clock source configuration: Dynamically and temporarily (not persistent to reboots): Permanently, adding clocksource= to the kernel stanza:
Is there a snapshot of Linux 2.6 clocksource?
Unfortunately, as the original snapshot of RHEL5 kernel was done at a time in which the actual linux-2.6 clocksource code was just being introduced for i386 and x86_64, it is not accurate to list the content of files into /sys/devices/system/clocksource/* directories in order to determine the current and the available system clock sources.
Where does the clock sit in a system?
When it comes to talk about a system’s clock, the hardware sits at the very bottom. Every typical system has several devices, usually implemented by clock chips, that provide timing features and can serve as clocks. So, which hardware is available depends on the particular architecture.