Messages in this thread | | | Date | Mon, 1 Dec 2008 10:59:56 +0000 | From | Russell King <> | Subject | Re: [ltt-dev] keypad/touchscreen driver events latencies using LTTng on ARM? |
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On Mon, Dec 01, 2008 at 05:57:37AM -0500, Mathieu Desnoyers wrote: > Ok, so for LTTng on ARM it would make sense to use the same clock source > as sched_clock for : > mach-pxa, mach-realview, mach-sa1100, mach-versatile, plat-omap. > > We basically have, for each of these build scenarios, to take the mmio > clock used by sched_clock and use it through > kernel/trace/trace-clock-32-to-64 to extend it to 64-bits. Therefore we > won't suffer from any of the constrains linked to cnt32_to_63 and we > would be sure that the trace clock is correct wrt SMP wrt memory > barriers and cache line bouncing because it uses per-cpu data to keep > the counters.
Just remember that MMIO clock sources are not available until after setup_arch() has finished - in other words, they don't work when the kernel initially boots. Accessing them too early will cause a page fault and hang the kernel.
-- Russell King Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/ maintainer of:
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