![]() ![]() But I'm seeing some systems sleep way longer (10+ milliseconds) than they should using an itimer. That is, since the hpet can't interrupt at exactly the frequency I want, the interrupts start to drift from wall time. And on some systems, the itimer provides periodic interrupts that are more stable over time. It would be nicer to use the itimer interface provided by Linux instead of interfacing with the hardware device driver directly. For example, on a Core 2 Quad, the example program included in the kernel documentation fails at HPET_IE_ON when set to poll. But I can't get it working on some machines that have hpet available as a clocksource either. Obviously I can't use it on machines that don't actually have a HPET. I'd like to sleep 1 millisecond or 250 microseconds between interrupts.Įnabling periodic interrupts from /dev/hpet works pretty well, but it doesn't seem to work on some machines. The second signal in such an event will be lost.I want to be interrupted at frequencies that are powers of ten, so enabling interrupts from /dev/rtc isn't ideal. ![]() Will expire before the signal from a previous expiration has beenĭelivered. It's thereforeĬonceivable that under pathologically heavy loading, ITIMER_REAL There each signal is permitted only one outstanding event. Gettimeofday(2), sigaction(2), signal(2) BUGS Under Linux, the generation and delivery of a signal are distinct, and On error, -1 is returned, and errno isĮRRORS EFAULT value or ovalue are not valid pointers.ĮINVAL which is not one of ITIMER_REAL, ITIMER_VIRT, or ITIMER_PROF.ĬONFORMING TO SVr4, 4.4BSD (This call first appeared in 4.2BSD). RETURN VALUE On success, zero is returned. Small time dependent on the system loading. Otherwise the delivery will be offset by a If the timer expires while the process isĪctive (always true for ITIMER_VIRT) the signal will be delivered immediately Upon expiration, a signal will be generatedĪnd the timer reset. Some short, constant time afterwards, dependent on the system timer Timers will never expire before the requested time, instead expiring ![]() Timer expires and it _ interval is zero) stops.īoth tv _ sec and tv _ usec are significant in determining the duration of ![]() A timer which is set to zero ( it _ value is zero or the Timers decrement from it _ value to zero, generate a signal, and reset to The old value of the timer is stored there. Sets the indicated timer to the value in value. Similarly, it_interval is set to the reset value. The element it_value is set to theĪmount of time remaining on the timer, or zero if the timer is disabled. Setting for the timer indicated by which (one of ITIMER_REAL, Getitimer(2) fills the structure indicated by value with the current Struct timeval it_value /* current value */ Struct timeval it_interval /* next value */ Timer values are defined by the following structures: The time spent by the application in user and kernel With ITIMER_VIRTUAL, this timer is usually used to profile System is executing on behalf of the process. ITIMER_PROF decrements both when the process executes and when the ITIMER_VIRTUAL decrements only when the process is executing, and ITIMER_REAL decrements in real time, and delivers SIGALRM upon expiration. Is sent to the process, and the timer (potentially) restarts. SYNOPSIS #include int getitimer(int which, struct itimerval * value ) int setitimer(int which, const struct itimerval * value, struct itimer- val * ovalue ) DESCRIPTION The system provides each process with three interval timers, eachĭecrementing in a distinct time domain. NAME getitimer, setitimer - get or set value of an interval timer Man pages -> Linux man pages -> getitimer (2) ![]()
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