Messages in this thread | | | Date | Thu, 22 Mar 2012 14:46:31 +0530 | Subject | Re: Not able to use HIGH_RES_TIMERS on ARM | From | Ajeet Yadav <> |
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Hi John, On our target ARCH_USES_GETTIMEOFFSET=y, can you please help me how can I useIRQSOFF_TRACER, PREEMPT_TRACER ?
On Wed, Mar 21, 2012 at 3:46 PM, Ajeet Yadav <ajeet.yadav.77@gmail.com> wrote: > 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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