netdev - Re: [PATCH net-next v4 3/4] sfc: support unicast PTP

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Message-ID: <Y/jbJ2lMShKZHh6Q@hoboy.vegasvil.org>
Date:   Fri, 24 Feb 2023 07:43:35 -0800
From:   Richard Cochran <richardcochran@...il.com>
To:     Íñigo Huguet <ihuguet@...hat.com>,
        Vadim Fedorenko <vadim.fedorenko@...ux.dev>,
        ecree.xilinx@...il.com, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org,
        Yalin Li <yalli@...hat.com>
Subject: Re: [PATCH net-next v4 3/4] sfc: support unicast PTP

On Fri, Feb 24, 2023 at 09:01:59AM +0000, Martin Habets wrote:
> On Wed, Feb 22, 2023 at 08:52:45AM -0800, Richard Cochran wrote:
> > The user space PTP stack must be handle out of order messages correct
> > (which ptp4l does do BTW).
> 
> This takes CPU time. If it can be avoided that is a good thing, as
> it puts less pressure on the host. It is not just about CPU load, it
> is also about latency.

It neither takes more CPU nor induces additional latency to handle
messages out of order.  The stack simply uses an event based state
machine.  In between events, the stack is sleeping on input.

Thanks,
Richard