netdev - Re: [PATCH net-next 08/11] net: ixgbe: convert to timecounter adjtime.

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Message-ID: <20141223214253.GA13937@localhost.localdomain>
Date:	Tue, 23 Dec 2014 22:42:53 +0100
From:	Richard Cochran <richardcochran@...il.com>
To:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Amir Vadai <amirv@...lanox.com>,
	Ariel Elior <ariel.elior@...gic.com>,
	Carolyn Wyborny <carolyn.wyborny@...el.com>,
	David Miller <davem@...emloft.net>,
	Frank Li <Frank.Li@...escale.com>,
	John Stultz <john.stultz@...aro.org>,
	Matthew Vick <matthew.vick@...el.com>,
	Miroslav Lichvar <mlichvar@...hat.com>,
	Mugunthan V N <mugunthanvnm@...com>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tom Lendacky <thomas.lendacky@....com>
Subject: Re: [PATCH net-next 08/11] net: ixgbe: convert to timecounter
 adjtime.

On Tue, Dec 23, 2014 at 01:07:19PM -0800, Jeff Kirsher wrote:
> Just for sanity sake, I will have Phillip test the changes, but there is
> no need to hold this up from being committed in the mean time.

FYI, here is a test that may show the improved behavior when comparing
before/after.

1. Start ptp4l, let it run long enough to find the frequency offset.

2. Stop ptp4l with ^C.

3. Wait a bit, to let the clock drift away.

4. Restart ptp4l, it will now start with the frequency offset learned
   in step 1.

5. Notice the the offsets in states s0 -> s1 -> s2.
   There will likely be less offset error with the patches applied.

Thanks,
Richard
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