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

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Date:   Fri, 24 Feb 2023 09:01:59 +0000
From:   Martin Habets <habetsm.xilinx@...il.com>
To:     Richard Cochran <richardcochran@...il.com>
Cc:     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 Wed, Feb 22, 2023 at 08:52:45AM -0800, Richard Cochran wrote:
> On Wed, Feb 22, 2023 at 03:41:51PM +0100, Íñigo Huguet wrote:
> 
> > The reason is explained in a comment in efx_ptp_insert_multicast filters:
> >    Must filter on both event and general ports to ensure
> >    that there is no packet re-ordering
> 
> There is nothing wrong with re-ordering.

I disagree. If re-ordering can be avoided that is a good thing.

> Nothing guarantees that
> datagrams are received in the order they are sent.

True, but they usually are.

> 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.

Martin