Sbs wrote:
Hi All, (Sorry if I am asking this on a wrong list. Please let me know the correct list for this question) We have a system which needs to be connected to a device that will produce an interrupt during every msec. So, we want interrupt latencies less than 1 msec (else we will miss interrupts). We tried measuring interrupt latencies with RT patch applied. However, the results that he got suggested that after applying patches, the worst case latency went up.
As I understand it, if you are doing your processing via interrupts, the your latency to start processing interrupts will increase on average with the PREEMPT_RT patch. There is additional scheduling overhead involved, and as Sven pointed out, if you don't bump the prio of the interrupt you care about, you can see MUCH higher latencies.
The PREEMPT_RT patch adds things like the rt-mutex replacement of most spinlocks, which adds preemption points and enable Priority Inheritance within the kernel, but this is all geared towards enable real-time applications. If you just want fast OS processing of interrupts, then mainline provides you with a nice non-preemptible kernel side interrupt implementation that won't be affected by things like applications :-)
Please slap me if I've misrepresented PREEMPT_RT somehow. (I'm sure no invitation is actually required ;-)
-- Darren Hart IBM Linux Technology Center Real-Time Linux Team -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
