netdev - RE: [EXT] Re: [PATCH v1] net: mvpp2: divide fifo for dts-active ports only

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Date:   Mon, 23 Nov 2020 15:44:05 +0000
From:   Stefan Chulski <stefanc@...vell.com>
To:     Russell King - ARM Linux admin <linux@...linux.org.uk>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "thomas.petazzoni@...tlin.com" <thomas.petazzoni@...tlin.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        Nadav Haklai <nadavh@...vell.com>,
        Yan Markman <ymarkman@...vell.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "mw@...ihalf.com" <mw@...ihalf.com>,
        "andrew@...n.ch" <andrew@...n.ch>
Subject: RE: [EXT] Re: [PATCH v1] net: mvpp2: divide fifo for dts-active ports
 only

> > > On Mon, Nov 23, 2020 at 04:52:40PM +0200, stefanc@...vell.com wrote:
> > > > From: Stefan Chulski <stefanc@...vell.com>
> > > >
> > > > Tx/Rx FIFO is a HW resource limited by total size, but shared by
> > > > all ports of same CP110 and impacting port-performance.
> > > > Do not divide the FIFO for ports which are not enabled in DTS, so
> > > > active ports could have more FIFO.
> > > >
> > > > The active port mapping should be done in probe before FIFO-init.
> > >
> > > It would be nice to know what the effect is from this - is it a
> > > small or large boost in performance?
> >
> > I didn't saw any significant improvement with LINUX bridge or
> > forwarding, but this reduced PPv2 overruns drops, reduced CRC sent errors
> with DPDK user space application.
> > So this improved zero loss throughput. Probably with XDP we would see a
> similar effect.
> >
> > > What is the effect when the ports on a CP110 are configured for 10G,
> > > 1G, and 2.5G in that order, as is the case on the Macchiatobin board?
> >
> > Macchiatobin has two CP's.  CP1 has 3 ports, so the distribution of FIFO would
> be the same as before.
> > On CP0 which has a single port, all FIFO would be allocated for 10G port.
> 
> Your code allocates for CP1:
> 
> 32K to port 0 (the 10G port on Macchiatobin) 8K to port 1 (the 1G dedicated
> ethernet port on Macchiatobin) 4K to port 2 (the 1G/2.5G SFP port on
> Macchiatobin)
> 
> I'm questioning that allocation for port 1 and 2.

Yes, but this allocation exists also in current code.
>From HW point of view(MAC and PPv2) maximum supported speed
in CP110: port 0 - 10G, port 1 - 2.5G, port 2 - 2.5G.
in CP115: port 0 - 10G, port 1 - 5G, port 2 - 2.5G.

So this allocation looks correct at least for CP115.
Problem that we cannot reallocate FIFO during runtime, after specific speed negotiation.

Regards.