netdev - Re: [PATCH net-next] ptp: add vclock timestamp conversion IOCTL

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Message-ID: <20211007201927.GA9326@hoboy.vegasvil.org>
Date:   Thu, 7 Oct 2021 13:19:27 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Sebastien Laveze <sebastien.laveze@....nxp.com>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        yangbo.lu@....com, yannick.vignon@....nxp.com,
        rui.sousa@....nxp.com
Subject: Re: [PATCH net-next] ptp: add vclock timestamp conversion IOCTL

On Thu, Oct 07, 2021 at 03:31:43PM +0200, Sebastien Laveze wrote:
> For example:
> Let's take a worst case, the PHC is adjusted every 10 ms, vclock every
> 1 sec with 1 ppm error.

You can't justify adjusting the HW clock and the vclocks
asynchronously with a single, isolated example.

If two independent processes are both adjusting a clock concurrently,
asynchronously, and at different control rates, the result will be
chaos.

It does not matter that it *might* work for some random setup of
yours.

The kernel has to function correctly in general, not just in some
special circumstances.

Thanks,
Richard