Messages in this thread | | | Date | Wed, 21 Mar 2012 15:46:39 +0530 | Subject | Re: Not able to use HIGH_RES_TIMERS on ARM | From | Ajeet Yadav <> |
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Hi John, Thank for clearing the confusion.
On Wed, Mar 21, 2012 at 10:28 AM, John Stultz <john.stultz@linaro.org> wrote: > On 03/19/2012 06:26 AM, Russell King - ARM Linux wrote: >> >> On Mon, Mar 19, 2012 at 06:49:34PM +0530, Ajeet Yadav wrote: >>> >>> Therefore our target configuration with 2.6 kernel was >>> GENERIC_CLOCKEVENTS=y, ARCH_USES_GETTIMEOFFSET=y, >> >> It's absolutely absurd to have a platform converted to use clockevents >> and clocksources, and then select ARCH_USES_GETTIMEOFFSET. That's saying >> "I provide the new infrastructure, but I want the dodgy old compatibility >> which doesn't work properly with a set of other features as well". >> >>> I conclude that GENERIC_CLOCKEVENTS is supported, hence I must set >>> ARCH_USES_GETTIMEOFFSET=n, in order to use NO_HZ, HIGH_RES_TIMERS, >>> IRQSOFF_TRACER, PREEMPT_TRACER >> >> Correct. If you're using clockevents and clocksources, you should not >> select ARCH_USES_GETTIMEOFFSET. >> > > Hey Ajeet, > As Russell pointed out, it looks like you're confused as to the use of > ARCH_USES_GETTIMEOFFSET. That option is only for legacy systems that don't > provide continuous clocksources that can be used for timekeeping. > > In the past, time was incremented by one tick every timer interrupt. Some > systems could use the timer hardware (usually PIT style decrementer) to > calculate inter-tick times. Its only for this style of hardware, that either > wraps or resets each tick, that GETTIMEOFFSET is needed. If you have a > continuous counter that doesn't wrap for a reasonable number of ticks, you > want to use the clocksource abstraction to represent that hardware. That has > the benefits of allowing high res timers and nohz, since we don't need to > keep a constant tick-beat to keep time (and also avoids lost-ticks and a > host of problems that tick based timekeeping can run into). > > So I suspect you probably want to verify your hardware supports a > clocksource and disable ARCH_USES_GETTIMEOFFSET. > > Sorry for any confusion! > > thanks > -john > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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