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

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Message-ID: <53C5F95E.6010300@linaro.org>
Date:	Tue, 15 Jul 2014 21:02:38 -0700
From:	John Stultz <john.stultz@...aro.org>
To:	Miroslav Lichvar <mlichvar@...hat.com>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Richard Cochran <richardcochran@...il.com>,
	Prarit Bhargava <prarit@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 0/3] timekeeping: Improved NOHZ frequency steering (v2)

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.

thanks
-john

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