Re: stmmac / meson8b-dwmac

From: Simon Huelck <simonmail@gmx.de>
To: Jose Abreu <jose.abreu@synopsys.com>,
	Sebastian Gottschall <s.gottschall@newmedia-net.de>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Cc: linux-amlogic@lists.infradead.org, netdev@vger.kernel.org,
	alexandre.torgue@st.com,
	Emiliano Ingrassia <ingrassia@epigenesys.com>,
	Gpeppe.cavallaro@st.com
Subject: Re: stmmac / meson8b-dwmac
Date: Wed, 27 Feb 2019 20:02:16 +0100	[thread overview]
Message-ID: <12d1d6de-2905-46a8-6481-d6f20c8e9d85@gmx.de> (raw)
In-Reply-To: <c21c30e9-e53e-02a5-c367-25898c4614e9@synopsys.com>

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

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