Messages in this thread | | | Date | Fri, 19 Mar 2010 13:07:10 +0300 | From | Ivan Kokshaysky <> | Subject | Re: [RFC][PATCH] Convert alpha to use clocksource |
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On Thu, Mar 18, 2010 at 03:19:18PM -0700, john stultz wrote: > On Fri, 2010-03-19 at 00:40 +0300, Ivan Kokshaysky wrote: > > Yeah, that looks cool. I'm typing this on the 800MHz UP1500 running > > 2.6.34-rc1 plus your patch, and the timekeeping works fine so far. > > Nice! Thanks for testing! Another benefit that I forgot to mention, is > that NTP adjustments will be made directly against the counter, instead > of being made against the tick. This avoids possible small errors at > tick time if the intertick interval doesn't match the actual tick > length. > > > > Though, even after a glance over the clocksource code, I've not > > gotten yet to how one could estimate the "shift" value... > > Any hints? > > Yea, selecting a good shift is obnoxious. You want to pick the largest > value of shift, so that it can be finely adjusted by ntp, but that > creates large mult values, which can cause overflows for large cycle > intervals. > > A function to solve this was actually recently added, but simply I > forgot to use it. :P
Understood. ;-)
> I actually should rework the register function so you just give it a > clocksource and a freq and it sets up both mult and shift for you. > > > > And if I recall correctly, production alphas have been clocked > > in the range of 60-1250 MHz. > > Cool. The shift value I picked should be ok then. But below is an > updated version that uses the self-calculated method.
Excellent. Thanks a lot!
> >From 078e91d14cb5e82a3fab00cf74faf45f44336590 Mon Sep 17 00:00:00 2001 > From: John Stultz <johnstul@us.ibm.com> > Date: Wed, 17 Mar 2010 12:43:11 -0700 > Subject: [PATCH] Convert alpha to use clocksources instead of arch_gettimeoffset > > Alpha has a tsc like rpcc counter that it uses to manage time. > This can be converted to an actual clocksource instead of utilizing > the arch_gettimeoffset method that is really only there for legacy > systems with no continuous counter. > > Further cleanups could be made if alpha converted to the clockevent model. > > I've not tested or compiled this code. Any help from the maintainers would > be greatly appreciated > > CC: Thomas Gleixner <tglx@linutronix.de> > CC: Richard Henderson <rth@twiddle.net> > CC: Ivan Kokshaysky <ink@jurassic.park.msu.ru> > CC: Matt Turner <mattst88@gmail.com> > Signed-off-by: John Stultz <johnstul@us.ibm.com>
Acked-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru> Tested-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Ivan.
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