Messages in this thread | | | Date | Mon, 1 Dec 2008 05:35:02 -0500 | From | Mathieu Desnoyers <> | Subject | Re: keypad/touchscreen driver events latencies using LTTng on ARM? |
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* Trilok Soni (soni.trilok@gmail.com) wrote: > Hi, > > I would like to try LTTng to measure the keypad and touchscreen > drivers events latency on ARM based board, which typically runs less > than 1GHz frequency. I have recently tried LTTng patches as per > compatibility list on LTTng website on 2.6.25 kernel on ARM11 based > board, but on LTTv it shows the IRQ min/max interval times on > nanoseconds precision, would that be correct? Because I thought it > could be possible to microseconds format until with hrtimers support > right? Just guide so that I can use this tool to effectively measure > driver latencies. Thanks. >
Hi Trilok,
The current Trace Clock implementation uses the generic fallback in include/asm-generic/trace-clock.h as a time source on ARM. It has a 1 jiffy precision and uses a logical clock in the least significant bits, incremented a each event, to keep track of the event order. Therefore, you should not rely on timing information more precise than 1 HZ.
However, I wonder if some of the newer ARM boards would happen to have a cycle counter (timestamp counter), so we could implement a get_cycles() and trace clock for them ?
Mathieu
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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