Where is jiffies incremented

So my question is:. As per my understanding the jiffies can not be per CPU otherwise the same process when scheduled on different CPU will see different jiffy value.

The global timer interrupts interrupt 0 fires once per jiffy, on any CPU. It increments jiffies. Note that the "Tickless Kernel" configuration option introduced in Linux 2. Serge Serge 7, 2 2 gold badges 19 19 silver badges 28 28 bronze badges.

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There was a very long thread about timers, jiffies, and related subjects in July of on the kernel mailing list. From eLinux. Jump to: navigation , search. Category : Kernel. Navigation menu Personal tools Log in Request account. Namespaces Page Discussion. Views Read View source View history. Where else to find us Twitter elinux elinux on Libera. Chat Facebook elinux. Jiffies for the Linux kernel variable unsigned long , which is used to record the system since its start, has been a much tick.

Once every timer interrupt occurs, Jiffies variable is incremented by one. Overflow how to do that? So until this moment overflow occurs it should be difficult. When the clock interrupt occurs, jiffies value is increased by one. Linux kernel provides the following four macros, which can effectively solve the case due to the overflow of jiffies caused by program logic error.

The following is culled from Linux Kernel 2. Kernel hardware provides various clock to provide time-dependent services, such as the busy-waiting wasted CPU cycles , and sleep-waiting abandoned CPU. Because jiffies clock ticking subject to change, it can not be optimized by the compiler should take volatile value. Setitimer user application and the getitimer controls the alarm signal is transmitted when the specified timeout occurs. RTC clock track absolute time. RTC battery often than computer survival.

RTC can be accomplished with the following functions: 1 read or set an absolute clock, and updates an interrupt is generated when the clock; 2 to be HZ 2HZ to generate periodic interrupts; 3 set alarms.