Engineering Elegance

Processes can be classified as either I/O-bound or processor-bound. As the name suggests, the former is a process where much of the time is spent in waiting for relatively slow I/O operations to complete. For instance, a process taking input for a word processor will be I/O-bound as it spends most of its time waiting for characters input. Such a process is runnable for only short duration, because it is eventually blocked to wait for more I/O. On the other hand, processor-bound process spends most of the Read more…

Having the understanding of HZ, jiffies, and system timer, it is appropriate to discuss the implementation of time management. Most of the jobs in time management are handled by a dedicated function called timer handler. In Microblaze, the kernel registers timer_interrupt as the interrupt handler: irqreturn_t TIMER_TEXT timer_interrupt(int irq, void *dev_id) { timer_ack(); write_seqlock(&xtime_lock); do_timer(1); update_process_times(user_mode(get_irq_regs())); profile_tick(CPU_PROFILING); write_sequnlock(&xtime_lock); return IRQ_HANDLED; } When kernel is executing timer handler, the timer is first acknowledged, followed by obtaining the xtime_lock lock, which protects access to jiffies and Read more…