linux-kernel - Re: [PATCH 0/3] net: microchip_t1s: additional phy support and collision detect handling

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Message-ID: <e4e675be-bbef-4fff-8bc2-d07bc1981ae2@lunn.ch>
Date:   Mon, 11 Dec 2023 14:54:49 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Ramón Nordin Rodriguez 
        <ramon.nordin.rodriguez@...roamp.se>
Cc:     Heiner Kallweit <hkallweit1@...il.com>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] net: microchip_t1s: additional phy support and
 collision detect handling

> ## with collision detection enabled
> 
> iperf3 normal
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.00  sec  5.54 MBytes  4.65 Mbits/sec    0             sender
> [  5]   0.00-10.01  sec  5.40 MBytes  4.53 Mbits/sec                  receiver
> 
> iperf3 reverse
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.00  sec   929 KBytes   761 Kbits/sec  293             sender
> [  5]   0.00-10.00  sec   830 KBytes   680 Kbits/sec                  receiver
> 
> 
> ## with collision detection disabled
> 
> iperf3 normal
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.00  sec  6.39 MBytes  5.36 Mbits/sec    0             sender
> [  5]   0.00-10.04  sec  6.19 MBytes  5.17 Mbits/sec                  receiver
> 
> iperf3 reverse
> - - - - - - - - - - - - - - - - - - - - - - - - -
> [ ID] Interval           Transfer     Bitrate         Retr
> [  5]   0.00-10.27  sec  1.10 MBytes   897 Kbits/sec  268             sender
> [  5]   0.00-10.00  sec  1.01 MBytes   843 Kbits/sec                  receiver
> 
> # Conclusions
> 
> The arm system running the lan865x macphy uses a not yet mainlined driver, see
> https://lore.kernel.org/all/20231023154649.45931-1-Parthiban.Veerasooran@microchip.com/
> 
> The lan865x driver crashed out every once in a while on reverse mode, there
> is definetly something biased in the driver for tx over rx.
>
> Then again it's not accepted yet.
> 
> Disabling collision detection seemes to have an positive effect.
> Slightly higher speeds and slightly fewer retransmissions.

I would want to first understand why there is such a big difference
with the direction. Is it TCP backing off because of the packet loss?
Or is there some other problem.

Maybe try with UDP streams, say with a bandwidth of 5Mbps. Do you
loose 4Mbps in one direction? Or a much smaller number of packets.

Are there any usable statistics? FCS errors?

    Andrew