netdev - Re: [PATCH net-next v2 1/2] qed: Add infrastructure for PTP support.

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Message-ID: <20170130132619.GA4854@localhost.localdomain>
Date:   Mon, 30 Jan 2017 14:26:19 +0100
From:   Richard Cochran <richardcochran@...il.com>
To:     "Mintz, Yuval" <Yuval.Mintz@...ium.com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Kalluru, Sudarsana" <Sudarsana.Kalluru@...ium.com>
Subject: Re: [PATCH net-next v2 1/2] qed: Add infrastructure for PTP support.

On Sun, Jan 29, 2017 at 09:36:11PM +0000, Mintz, Yuval wrote:
> I might have gotten it all wrong, but I was under the assumption that time-
> stamped packets are periodic, and that the interval between two isn't
> going to be so small.

That is an incorrect assumption.  Consider the Delay_Req packets
arriving on a port in the MASTER state.

> Is so, how does having a couple of additional instructions in between
> jeopardizes the next time stamp?

It is not just about the few instructions, but there is also
preemption possible.

Thanks,
Richard