Low network throughput on i.MX28

[Jörg Krause]

Hi Shawn,

On Wed, 2016-11-02 at 09:24 +0100, Stefan Wahren wrote:
> Am 02.11.2016 um 09:14 schrieb Jörg Krause:
> > On Sat, 2016-10-29 at 11:08 +0200, Stefan Wahren wrote:
> > > > Jörg Krause <joerg.krause at embedded.rocks> hat am 29. Oktober
> > > > 2016
> > > > um 01:07
> > > > geschrieben:
> > > > 
> > > > 
> > > > You mentioned [1] an optimization in the Freescale vendor Linux
> > > > kernel
> > > > [2]. I would really like to see this optimization in the
> > > > mainline
> > > > kernel.
> > > > 
> > > > Did you ever tried to port this code from Freescale to
> > > > mainline?
> > > 
> > > Yes, i tried once but i was frustrated soon because of the lot of
> > > required
> > > changes and resulting issues.
> > 
> > I got the PIO mode working for the mxs-mmc driver. For this I
> > ported
> > the PIO code from the vendor kernel and removed the usage of the
> > DMA
> > engine entirely.
> 
> Good job
> 
> > 
> > Testing network bandwidth with iperf, I get about ~10Mbit/sec with
> > PIO
> > mode compared to ~6.5Mbit/sec with DMA mode for UDP and about
> > ~6.5Mbit/sec compared to ~4.5Mbit/sec with DMA mode for TCP.
> 
> And how about MMC / sd card performance?

I noticed poor performance with the i.MX28 MMC and/or DMA driver using
the mainline kernel compared to the vendor Freescale kernel 2.6.35.
I've seen that hou have added the drivers to mainline some years ago.

My custom i.MX28 board has a wifi chip attached to the SSP2 interface.
Comparing the bandwith with iperf I get >20Mbits/sec on the vendor
kernel and <5Mbits/sec on the mainline kernel.

My best guess is that there is some kind of bottleneck in the drivers.
I already started looking at the vendor drivers as well as at the
mainline drivers, but I need some more investigation to understand the
complexity.

Do you have any idea what the bottleneck might be?

Best regards,
Jörg Krause