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Adventurer
Adventurer
258 Views
Registered: ‎09-30-2014

Relatively slow performance under Petalinux

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We have two seperate custom designed board using Zynq Ultrascale+ devices (two different size parts).  In one design the Zynq's GEM RGMII interface is connected to a TI DP83867.  The other design we tie direct to a RGMII port on an multiport ethernet switch.  In both cases, we can only get between 180 Mbps and 220 Mbps out of the Zynq Ultrascale+.  We have tried different host computers for testing to insure it isn't any software on the host and given the different phy setups, it leads us to believe it is something on the Linux (Petalinux side).  

We are looking for suggestions on how to speed up the ethernet interfaces under Linux.  Any help would be appreciated.

Both sets of hardware are being tested with Petalinux 2018.3.

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Adventurer
Adventurer
97 Views
Registered: ‎09-30-2014

Re: Relatively slow performance under Petalinux

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The primary issue was related to a little paid attention to clock setting in Vivado.  The "TIMESTAMP" clock in the clock output sections of Vivado influences the CPU scheduler in Linux.  When changing it from 33.333 MHz to 100 MHz, most of my bandwidth problems were solved. 

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Adventurer
Adventurer
175 Views
Registered: ‎09-30-2014

Re: Relatively slow performance under Petalinux

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A little more info.  Tested using both iperf2 and iperf3 on Petalinux to external computer running iperf2 and iperf3.  

The Zynq Ultrascale+ (with both iperf2 and iperf3) achieves about 200 Mbps on transmit and 400 Mbps on receive.  Still don't know where to look.  Any help would be great.

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Adventurer
Adventurer
138 Views
Registered: ‎09-30-2014

Re: Relatively slow performance under Petalinux

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I have now tested with iperf and the base metal iperf test in the Xilinx SDK.  With the bare metal lwIP TCP tests, I can get around 900 Mbps each direction.  This points to a Linux configuration issue slowing the performance down to 400 Mbps for RX and 200 Mbps for TX.  

Does anyone have suggestions of what in Linux (device tree, some timer, etc) might be causing the performance to degrade that much?

Explorer
Explorer
121 Views
Registered: ‎04-19-2018

Re: Relatively slow performance under Petalinux

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I assume you don't have lots of sw on that linux. Then my next suspicion would be on buffer size. Imagine your PHY and all the stuff is capable of swallowing close to 1 G as you could wish, is there space for that much between processing slots? If there isn't something may just stall and data rate drops *clunk*

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Adventurer
Adventurer
98 Views
Registered: ‎09-30-2014

Re: Relatively slow performance under Petalinux

Jump to solution

The primary issue was related to a little paid attention to clock setting in Vivado.  The "TIMESTAMP" clock in the clock output sections of Vivado influences the CPU scheduler in Linux.  When changing it from 33.333 MHz to 100 MHz, most of my bandwidth problems were solved. 

View solution in original post

Explorer
Explorer
76 Views
Registered: ‎04-19-2018

Re: Relatively slow performance under Petalinux

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Good to know if I ever run in similar problems

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