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Date: Wed, 25 Jan 2012 13:46:18 +0400 From: Dmitry Antipov <dmitry.antipov@...aro.org> To: john stultz <johnstul@...ibm.com> CC: linaro-dev@...ts.linaro.org, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Amit Kucheria <amit.kucheria@...aro.org> Subject: Re: [PATCH] hrtimers, timers: eliminate some jiffies-backed code On 01/25/2012 04:01 AM, john stultz wrote: > Why do you want to move loops like the above from jiffies based timeouts > to hrtimers? I'm trying to see whether there are possible benefits in the sense of power management. More hrtimers with larger expire deltas -> more opportunities to coalesce hrtimer interrupts -> less frequency of hrtimer interrupts -> longer idle/suspend/stanby/etc. periods. > Is there an actual need for sub-jiffy granularity in these sorts of > timeouts? I didn't collect a representative statistics among the large set of different drivers, but I believe the answer is 'no' for the most of them. The main reason is described above. > Or is this really just a "getting away from using jiffies" cleanup? A bit of this too, definitely. Documentation/timers/highres.txt notices 'complete jiffies removal' as something which may take place sometime; at least, I don't have an ideas why to use jiffies in a new code. > Calling get_time() again on each hrtimer_wakeup isn't free. > > With this we end up when the irq fires, calling hrtimer_interrupt, which > reads the time and goes through the timer list running expired timers, > which then runs the sleeper's timer which then reads the time again! > Additinoally, this extra overhead is done even no one wants the elapsed > time. Thanks, I'll think about reworking of this. Dmitry -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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