linux-kernel - Re: [PATCH v2 1/2] timekeeping: add EXPORT_SYMBOL_GPL for do

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Date:	Wed, 22 Oct 2014 14:42:09 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Mike Surcouf <mps.surcouf.lkml@...il.com>
cc:	Thomas Shao <huishao@...rosoft.com>,
	Richard Cochran <richardcochran@...il.com>,
	Jeff Epler <jepler@...ythonic.net>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"olaf@...fle.de" <olaf@...fle.de>,
	"apw@...onical.com" <apw@...onical.com>,
	"jasowang@...hat.com" <jasowang@...hat.com>,
	KY Srinivasan <kys@...rosoft.com>,
	John Stultz <john.stultz@...aro.org>,
	Richard Cochran <rcochran@...utronix.de>
Subject: Re: [PATCH v2 1/2] timekeeping: add EXPORT_SYMBOL_GPL for
 do_adjtimex()

On Wed, 22 Oct 2014, Mike Surcouf wrote:

> I get that NTP can be installed locally.  This is how I regulate time
> on my guests.  I agree the admin argument probably doesn't stand up.
> 
> The problem is hyperv_clocksource (pluggable time source used by
> hyperv guests) is systematically fast in my environment. by around
> -250 PPM.
> I get away with NTP (just).
> However others have had to use tickadj to get hyperv_clocksource close
> enough for NTP to work i.e. inside +/-500 PPM. (This IS outside normal
> admin tasks)
> 
> So if we are going to use NTP as the solution for hyperv guests (which
> is a valid one) the systematic drift of hyperv_clocksource in
> different environments will need to be addressed.  Maybe this patch
> could be modified to tune the tick count on boot before NTP starts and
> then leave it alone so NTP can take over.

How about fixing hyperv_clocksource in the first place?

Thanks,

	tglx
 
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