netdev - Re: stmmac / meson8b-dwmac

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Date:   Wed, 27 Feb 2019 20:02:16 +0100
From:   Simon Huelck <simonmail@....de>
To:     Jose Abreu <jose.abreu@...opsys.com>,
        Sebastian Gottschall <s.gottschall@...media-net.de>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     linux-amlogic@...ts.infradead.org, Gpeppe.cavallaro@...com,
        alexandre.torgue@...com,
        Emiliano Ingrassia <ingrassia@...genesys.com>,
        netdev@...r.kernel.org
Subject: Re: stmmac / meson8b-dwmac

Hi,

the thing is , that im not a stmmac developer. Yes , maybe i can bissect
it and yes you are lucky since im a C-developer since a long time for
embedded systems.

The problem is that i dont understand the structure of stmmac and im not
aware of any documentation about the driver structure nor the underlying
ethernet hardware ( even though im used to ethernet hardware in embedded
environment ). So how shall i recognize the relevant change between
4.14.29 and 5.0rc8 ?

Is it in the DTS/DTB, wrong hardware description ? Is it in the code ?
how is the duplex hardware working on this piece ?

I can try to support you the best i can, but i have little chances to
analyze it myself. At which measurements / counters is it possible to
see that duplex is fully working ?  Why did even the non-duplex
bandwidth regress from 900MBits to 650 ? Why is that 650 MBits dividing
up to TX and RX in summary when doing duplex ? Why is TX not starving in
duplex but RX ?

>From my point of view should be the following things given:
- the non duplex bandwidth should be somewhere around 900MBits , the HW
is capable of that
- TX should not influence RX or vice versa in duplex
- the duplex bandwidth should be 900MBits in both directions ( maybe a
bit asymetric when buffers in both dirs are not same )

I guess we need some profiling on stmmac and ( at least i need ) more
knowledge of the hardware and stmmac itself. Can someone point me to the
driver documentation, describing the functions in the code and the
structure ? How can i profile stmmac ( usually im using hardware / JTAG
debuggers at work, but here @home i got nothing like that )

So how do we continue ?

regards,
Simon

Am 27.02.2019 um 12:09 schrieb Jose Abreu:
> Hi Simon,
>
> On 2/24/2019 8:34 PM, Simon Huelck wrote:
>> the topic is about ODROID C2 / Amlogic S905X since the start. we have a
>> performance regression since 4.14.
> As we are not advancing in this topic I suggest you try bisecting
> the offending commit.
>
> Thanks,
> Jose Miguel Abreu