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Altera_Forum
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16 years ago

Ethernet performance using TSE in uClinux

Hi all, I am measuring ethernet performance on a NIOS II based board with an Altera TSE IP Core running uClinux, and it's been disappointing so far. I've done timing using TCP and UDP, and bar...
Altera_Forum's avatar
Altera_Forum
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15 years ago

An update:

I fixed all or most of the problems in the driver that were causing TCP errors or slow downs and also added some optimizations with help from the FPGA engineer.

Now I get:

UDP TX 46 MBit/s, tested with 50x1KiB messages

TCP TX 38 MBit/s, TCP RX 54 MBit/s with 32KiB socket buffers, 30x128KiB messages

The changes:

  • 110MHz processor with 32KiB caches.

  • Updated altera_tse.c. There was a fix in December to reschedule NAPI if there are more descriptors to process. I also changed it to disable IRQs again in this case, I think that is the correct behavior for NAPI.

  • TX and RX checksum offload. This is done with a custom FPGA component doing the checksums between the SGDMA and the MAC. Linux has some support for checksum offload, but I had to do hack out some of the checksum calls in the TCP/IP stack to get it to never waste time on them.

  • Scatter-gather (NETIF_F_SG) support in the driver. Checksum offload was necessary for this, Linux won't support one without the other. Unaligned transfer support on the SGDMA was also necessary.

  • Define NO_TX_IRQ in the driver and fix it to work without a TX interrupt.

  • This is actually the important part. To get the driver to correctly work with scatter gather and no TX interrupt, I had to fix it to only restart the SGDMA in one place. Since the SGDMA doesn't provide any feedback on the descriptor it last processed, and it turned out to be very difficult to correctly keep track of this, I have to walk part of the descriptor list in the transmit function to start the SGDMA in the right place. Only restarting the SGDMA in one place made it more reliable and a lock on the TX ring is no longer needed.

  • Cut out some error checking in the driver.

One remaining issue is that the SGDMA always preloads the next descriptor. Which I think means it will load the next descriptor for a packet that is not set up yet, but will be soon, see that it is not owned by hardware, and stop. In practice, this means it stops after sending each packet, when it may not be necessary. Unfortunately there doesn't seem to be a way to turn off this "feature".

I'm attaching a diff of my version of the driver against unstable-nios2mmu in case it's useful to someone.