linux-kernel - Re: [PATCH 0/3] timekeeping: Improved NOHZ frequency steering (v2)

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Date:	Wed, 16 Jul 2014 08:59:07 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	John Stultz <john.stultz@...aro.org>
cc:	Miroslav Lichvar <mlichvar@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>
Subject: Re: [PATCH 0/3] timekeeping: Improved NOHZ frequency steering (v2)

On Tue, 15 Jul 2014, John Stultz wrote:

> On 07/08/2014 04:08 AM, Miroslav Lichvar wrote:
> > On Mon, May 19, 2014 at 10:57:29AM -0700, John Stultz wrote:
> >> Another area we have to be careful with is there are still
> >> architectures (powerpc and ia64) which haven't switched from the old
> >> vsyscall rounding logic (CONFIG_GENERIC_TIME_VSYSCALL_OLD). In these
> >> cases we add up to 1ns of error each tick/update as we round up the
> >> sub-nanoseconds to ensure we don't see inconsistencies.  If the
> >> adjustment logic can't handle this, I don't want to regress those
> >> arches.
> > I spent some time trying to figure out a workaround for the nanosecond
> > rounding, but I didn't find anything that wouldn't complicate the mult
> > adjustment logic and bring back the problems which the direct division
> > approach is supposed to solve.
> >
> > It seems it may be a while before the old vsyscalls are fixed. How
> > about including only the first two patches from this set for now?
> 
> Hey! Sorry for the slow response here, I was on the road the last two weeks.
> 
> So thanks for the ping here. If you're happy with the first two as an
> initial step, I'd be willing to try to push those in. The only trouble
> is there's a whole lot of timekeeping churn headed for 3.17 that Thomas
> has cooked up. While there isn't likely to be direct conflicts in the
> changes, I get nervous about mixing too many changes in subtle code at once.
> 
> But maybe I'm being overly cautious?
> 
> Thomas: Would you be ok if I push you some patches to improve ntp/ptp
> freq steering w/ NOHZ for this merge window as well? So far the patches
> have only shown nice improvements and no regressions, but its clearly
> subtle code, and there's a lot going on in this merge window.

I think it's ok. The steering is orthogonal to the other stuff cooking.

Thanks,

	tglx
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