I need a timer tick with 1ms resolution under linux. It is used to increment a timer value that in turn is used to see if various Events should be triggered. The POSIX timerfd_create is not an option because of the glibc requirement. I tried timer_create and timer_settimer, but the best I get from them is a 10ms resolution, smaller values seem to default to 10ms resolution. Getittimer and setitimer have a 10 ms resolution according to the manpage.
The only way to do this timer I can currently think of is to use clock_gettime with CLOCK_MONOTONIC in my main loop an test if a ms has passed, and if so to increase the counter (and then check if the various Events should fire).
Is there a better way to do this than to constantly query in the main loop? What is the recommended solution to this?
The language I am using is plain old c
Update
I am using a 2.6.26 Kernel. I know you can have it interrupt at 1kHz, and the POSIX timer_* functions then can be programmed to up to 1ms but that seems not to be reliable and I don’t want to use that, because it may need a new kernel on some Systems. Some stock Kernel seem to still have the 100Hz configured. And I would need to detect that. The application may be run on something else than my System 🙂
I can not sleep for 1ms because there may be network events I have to react to.
How I resolved it Since it is not that important I simply declared that the global timer has a 100ms resolution. All events using their own timer have to set at least 100ms for timer expiration. I was more or less wondering if there would be a better way, hence the question.
Why I accepted the answer I think the answer from freespace best described why it is not really possible without a realtime Linux System.
Polling in the main loop isn’t an answer either – your process might not get much CPU time, so more than 10ms will elapse before your code gets to run, rendering it moot.
10ms is about the standard timer resolution for most non-realtime operating systems (RTOS). But it is moot in a non-RTOS – the behaviour of the scheduler and dispatcher is going to greatly influence how quickly you can respond to a timer expiring. For example even suppose you had a sub 10ms resolution timer, you can’t respond to the timer expiring if your code isn’t running. Since you can’t predict when your code is going to run, you can’t respond to timer expiration accurately.
There is of course realtime linux kernels, see http://www.linuxdevices.com/articles/AT8073314981.html for a list. A RTOS offers facilities whereby you can get soft or hard guarantees about when your code is going to run. This is about the only way to reliably and accurately respond to timers expiring etc.