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

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Message-ID: <1268934923.1855.8.camel@work-vm>
Date:	Thu, 18 Mar 2010 10:55:23 -0700
From:	john stultz <johnstul@...ibm.com>
To:	Richard Henderson <rth@...ddle.net>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ivan Kokshaysky <ink@...assic.park.msu.ru>,
	Matt Turner <mattst88@...il.com>
Subject: Re: [RFC][PATCH] Convert alpha to use clocksource

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.

However, I'm not maintaining the arch, and this patch isn't limiting the
timekeeping core, so the call is really yours. I sent this out on a whim
since it looked easy to do.

However, while this change is totally optional, I suspect my suggestion
about moving to the clockevents code is going to rise in importance. The
triplicate timer code paths of non-converted, converted periodic and
converted one-shot is difficult to follow.

I'll try to find a good example of an easy conversion case (PIT on x86
is not it) and send it your way.

thanks
-john

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