linux-kernel - Re: [PATCH v2] net: mvneta: Fix Serdes configuration for 2.5Gbps modes

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Date:   Fri, 12 Jun 2020 14:02:50 +0100
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Sascha Hauer <s.hauer@...gutronix.de>
Cc:     linux-arm-kernel@...ts.infradead.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        kernel@...gutronix.de
Subject: Re: [PATCH v2] net: mvneta: Fix Serdes configuration for 2.5Gbps
 modes

On Fri, Jun 12, 2020 at 01:52:50PM +0200, Sascha Hauer wrote:
> On Fri, Jun 12, 2020 at 12:30:31PM +0100, Russell King - ARM Linux admin wrote:
> > On Fri, Jun 12, 2020 at 12:22:13PM +0100, Russell King - ARM Linux admin wrote:
> > > On Fri, Jun 12, 2020 at 11:42:08AM +0100, Russell King - ARM Linux admin wrote:
> > > > With the obvious mistakes fixed (extraneous 'i' and lack of default
> > > > case), it seems to still work on Armada 388 Clearfog Pro with 2.5G
> > > > modules.
> > > 
> > > ... and the other bug fixed - mvneta_comphy_init() needs to be passed
> > > the interface mode.
> > 
> > Unrelated to the patch, has anyone noticed that mvneta's performance
> > seems to have reduced?  I've only just noticed it (which makes 2.5Gbps
> > rather pointless).  This is iperf between two clearfogs with a 2.5G
> > fibre link:
> > 
> > root@...arfog21:~# iperf -V -c fe80::250:43ff:fe02:303%eno2
> > ------------------------------------------------------------
> > Client connecting to fe80::250:43ff:fe02:303%eno2, TCP port 5001
> > TCP window size: 43.8 KByte (default)
> > ------------------------------------------------------------
> > [  3] local fe80::250:43ff:fe21:203 port 48928 connected with fe80::250:43ff:fe02:303 port 5001
> > [ ID] Interval       Transfer     Bandwidth
> > [  3]  0.0-10.0 sec   553 MBytes   464 Mbits/sec
> > 
> > I checked with Jon Nettleton, and he confirms my recollection that
> > mvneta on Armada 388 used to be able to fill a 2.5Gbps link.
> > 
> > If Armada 388 can't manage, then I suspect Armada XP will have worse
> > performance being an earlier revision SoC.
> 
> I only have one board with a Armada XP here which has a loopback cable
> between two ports. It gives me:
> 
> [  3] local 172.16.1.4 port 47002 connected with 172.16.1.0 port 5001
> [ ID] Interval       Transfer     Bandwidth
> [  3]  0.0-10.0 sec  1.27 GBytes  1.09 Gbits/sec
> 
> Still not 2.5Gbps, but at least twice the data rate you get, plus my
> board has to handle both ends of the link.

It turns out I still had various locking debugs and DMA API debug
enabled:

[  3] local fe80::250:43ff:fe21:203 port 39326 connected with fe80::250:43ff:fe02:303 port 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  2.70 GBytes  2.32 Gbits/sec

... which is more like it for this platform!

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!