linux-kernel - Re: [RFC][patch 1/5] move clock source related code to clocksource.c

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Message-ID: <20090723095336.2cb4b1a4@skybase>
Date:	Thu, 23 Jul 2009 09:53:36 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	john stultz <johnstul@...ibm.com>
Cc:	Daniel Walker <dwalker@...o99.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC][patch 1/5] move clock source related code to
 clocksource.c

On Wed, 22 Jul 2009 17:28:20 -0700
john stultz <johnstul@...ibm.com> wrote:

> Hey Martin,
> 	So here's a really quick swipe at breaking apart the clocksource struct
> into a clocksource only portion and a timekeeping portion.
> 
> Caveats:
> 1) This doesn't completely build. The core bits do, but there's still a
> few left-over issues (see following caveats). Its just here to give you
> an idea of what I'm thinking about. I'd of course break it up into more
> manageable chunks before submitting it.
> 
> 2) Structure names aren't too great right now. Not sure timeclock is
> what I want to use, probably system_time or something. Will find/replace
> before the next revision is sent out.
> 
> 3) I still need to unify the clocksource and cyclecounter structures, as
> they're basically redundant now.
> 
> 4) I still need to fix the update_vsyscall code (shouldn't be hard, I
> didn't want to run through arch code yet).
> 
> 5) The TSC clocksource uses cycles_last to avoid very slight skew issues
> (that otherwise would not be noticed). Not sure how to fix that if we're
> pulling cycles_last (which is purely timekeeping state) out of the
> clocksource. Will have to think of something.
> 
> 
> Other cleanups still out there in the distant future:
> 1) Once all arches are converted to GENERIC_TIME, we can remove the
> ifdefs, and cleanup a lot of the more complicated xtime struct
> manipulation. It will cleanup update_wall_time() nicely.
> 
> 2) I have a logarithmic accumulation patch to update_wall_time that will
> remove the need for xtime_cache to be managed and updated. Just have to
> spend some additional time making sure its bugfree.
> 
> 3) Once all arches are converted to using read_persistent_clock(), then
> the arch specific time initialization can be dropped. Removing the
> majority of direct xtime structure accesses.
> 
> 4) Then once the remaining direct wall_to_monotonic and xtime accessors
> are moved to timekeeping.c we can make those both static and embed them
> into the core timekeeping structure.
> 
> 
> But let me know if this patch doesn't achieve most of the cleanup you
> wanted to see.

Cool, I'll have a look. What I can see right away is that a lot of the
changes I tried yesterday are contained in your patch as well.
But your patch is more radical, a lot more is (re-)moved from the
struct clocksource. That mult_orig goes aways is good :-)

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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