linux-kernel - Re: [RFC][PATCH] Convert alpha to use clocksource

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Message-ID: <20100318214030.GA8934@jurassic.park.msu.ru>
Date:	Fri, 19 Mar 2010 00:40:30 +0300
From:	Ivan Kokshaysky <ink@...assic.park.msu.ru>
To:	john stultz <johnstul@...ibm.com>
Cc:	Richard Henderson <rth@...ddle.net>,
	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Matt Turner <mattst88@...il.com>
Subject: Re: [RFC][PATCH] Convert alpha to use clocksource

On Thu, Mar 18, 2010 at 10:55:23AM -0700, john stultz wrote:
> On Thu, 2010-03-18 at 07:32 -0700, Richard Henderson wrote:
> > On 03/17/2010 07:01 PM, John Stultz wrote:
> > > 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.
> > 
> > With 8 seconds or less between roll-overs, do you actually consider
> > this a continuous counter?  I don't.  I suggest this be left alone.
> 
> The timekeeping code handles this (although the shift value I picked may
> need some adjustment - what is the expected counter freq range on
> alpha?). The ACPI PM counter which is very common on x86 is only 24 bits
> and rolls over in ~5 seconds. It works fine.

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.

Though, even after a glance over the clocksource code, I've not
gotten yet to how one could estimate the "shift" value...
Any hints?

And if I recall correctly, production alphas have been clocked
in the range of 60-1250 MHz.

Ivan.
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