[meta-xilinx] Ethernet Transfer Speed Question

[Joe Nicholson]

Hi Nathan et al

 

I've a question regarding data transfer speed over Ethernet using the Xilinx
3.14 kernel built from the meta-xilinx layer.

 

We've previously been using a 'custom' 3.9 kernel (basically a slightly
customised Xilinx kernel, with a couple of new drivers. no important
changes).

We're keen to move to the standard Xilinx 3.14 kernel as built from
meta-xilinx.  Our target is zc702-zynq7.

 

On the 3.9 kernel, an iperf test of data transfer over the Ethernet gives a
massively respectable 480Mbits/second!

On the 3.14 kernel, however, the same test gives just 327Mbits/second.

 

327Mbits/second is OK, but still much lower than the Xilinx 3.9 kernel.  

I tried make oldconfig of the old 3.9 kernel configuration used that instead
of the default config, but had the same result.

 

Is it possible that the Ethernet driver has had some speed retardation in
the driver recently, between 3.9 and 3.14?  Any pointers would be helpful.

In reality I think we can probably cope with 327Mbits/second, however the
customer's initial tests were on the 3.9 kernel... so I'm keen to trace the
point of the speed reduction.

 

On a similar issue, I tried the Daisy branch of meta-xilinx with the 3.14
kernel - it achieves only 107Mbit/second!!

I traced this down to CONFIG_DEBUG_WW_MUTEX_SLOWPATH=y and a few other
similar debugging options being switched on by default.  These are all
nicely switch off in the Dizzy branch.

 

So really, I'm keen to understand why the Ethernet transfer speed of the
zc702 appears to have slowed down and whether there's anything I can do to
speed it back up!

.e.g. move to Fido and a 3.17 kernel :)

 

Cheers!

 

Joe Nicholson

 

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