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

[Russell King - ARM Linux admin <linux@armlinux.org.uk>]

On Mon, Nov 23, 2020 at 03:26:11PM +0000, Stefan Chulski wrote:
> > -----Original Message-----
> > From: Russell King - ARM Linux admin <linux@armlinux.org.uk>
> > Sent: Monday, November 23, 2020 5:11 PM
> > To: Stefan Chulski <stefanc@marvell.com>
> > Cc: netdev@vger.kernel.org; thomas.petazzoni@bootlin.com;
> > davem@davemloft.net; Nadav Haklai <nadavh@marvell.com>; Yan Markman
> > <ymarkman@marvell.com>; linux-kernel@vger.kernel.org; kuba@kernel.org;
> > mw@semihalf.com; antoine.tenart@bootlin.com; andrew@lunn.ch
> > Subject: [EXT] Re: [PATCH v1] net: mvpp2: divide fifo for dts-active ports only
> > 
> > External Email
> > 
> > ----------------------------------------------------------------------
> > Hi,
> > 
> > On Mon, Nov 23, 2020 at 04:52:40PM +0200, stefanc@marvell.com wrote:
> > > From: Stefan Chulski <stefanc@marvell.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.

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