From: Richard Cochran <richardcochran@gmail.com>
To: Kshitiz Gupta <kshitiz.gupta@ni.com>
Cc: jeffrey.t.kirsher@intel.com, intel-wired-lan@lists.osuosl.org,
netdev@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH RFC net-next] igb: adjust SYSTIM register using TIMADJ register
Date: Fri, 20 Apr 2018 14:12:10 -0700 [thread overview]
Message-ID: <20180420211210.43oyqmqoho6gdnfh@localhost> (raw)
In-Reply-To: <1524254196-21705-1-git-send-email-kshitiz.gupta@ni.com>
On Fri, Apr 20, 2018 at 02:56:36PM -0500, Kshitiz Gupta wrote:
> Currently the driver adjusts time by reading the current time and then
> modifying it before writing to SYSTIM register. This can introduce
> inaccuracies in SYSTIM. With a PREEMPT_RT kernel, spinlocks may be
> interrupted, which in the existing implementation may lead to increased
> time between the read and the write.
>
> Alternatively as per section 7.8.3.2 in the i210 data sheet, this
> operation can be done more accurately by using the TIMADJ registers,
> but this should only be used for adjustments less than one 8th of the
> sync interval. Once this register is written, the software can poll on
> TSICR.TADJ to make sure that adjustment operation is completed.
I doubt the utility of this. The first jump is typically to correct a
large offset of seconds, minutes, or even months. After that, the
servo corrects any remaining error.
It would help if you would show us a clearly improved servo response
with this change applied.
Thanks,
Richard
prev parent reply other threads:[~2018-04-20 21:12 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-20 19:56 [PATCH RFC net-next] igb: adjust SYSTIM register using TIMADJ register Kshitiz Gupta
2018-04-20 21:12 ` Richard Cochran [this message]
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