netdev - Re: [RFC PATCH 6/9] net: dsa: hellcreek: Add debugging mechanisms

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Message-ID: <87k0zynwqj.fsf@kurt>
Date:   Tue, 23 Jun 2020 08:04:52 +0200
From:   Kurt Kanzenbach <kurt@...utronix.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        netdev <netdev@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "open list\:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Richard Cochran <richardcochran@...il.com>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [RFC PATCH 6/9] net: dsa: hellcreek: Add debugging mechanisms

Hi Vladimir,

On Mon Jun 22 2020, Vladimir Oltean wrote:
> Hi Kurt,
>
> On Mon, 22 Jun 2020 at 15:34, Kurt Kanzenbach <kurt@...utronix.de> wrote:
>>
>>  * Re-prioritization of packets based on the ether type (not mac address)
>
> This can be done by offloading a tc skbedit priority action, and a
> "protocol" key (even though I don't understand why you need to mention
> "not mac address".

Thanks. That seems like it can be used. I did mention the mac address,
because the switch has two ways of doing a re-prioritization either by
fdb entries via mac addresses or by the high level inspection (HLI)
based on the ether type.

>
>>  * Packet logging (-> retrieval of packet time stamps) based on port, traffic class and direction
>
> What does this mean? tcpdump can give you this, for traffic destined
> to the CPU. Do you want to mirror/sample traffic to the CPU for debug?
>

The switch can capture timestamps (nanoseconds) when packets have been
transmitted or received on all ports. The timestamps are stored in a
FIFO and can be retrieved later. As you said tcpdump only works for
packets at the CPU port. This feature is useful for debugging latency
issues for specific traffic flows.

Thanks,
Kurt

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