DSPC-8681 PCIe Throughput

YC, Tsai

Hi,

I have DSPC8681 with 4 C6678 DSP, and run Desktop Linux SDK filtestdemo Application.

The test file size is 1.2GB(1,181,272,546 bytes).

I used DMA and the time measured is 3645951 us (3.6 seconds). It means that DSPC-8681 PCIe throughput is 328MB/s.

I have reviewed "Throughput Performance Guide for C66x KeyStone Devices"(SPRABK5A1) and there are three main factors affecting PCIe throughput performance -Overhead, Packet size and EDMA. It's for Keystone but not DSPC-8681, right?

My question is:

DSPC-8681 has PLX PEX8624 PCie Switch which supports maximum payload size 2048 bytes

For inbound transactions, the PCIe v2 specification permits data payloads up to 4096
bytes; however, in KeyStone devices, the maximum PCIe data payload size is limited to
256 bytes for inbound transactions. How about the maximum PCie data payload size of DSPC-8681?

For outbound transfers, the Keystone PCIe peripheral is able to transfer packets of up
to 128 bytes. How about DSPC-8681?

over 12 years ago

0 Raja over 12 years ago

TI__Guru* 81335 points

Hi,

Please refer below thread which discuss about DSPC-8681 PCIe speed.

http://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/639/t/211448.aspx

I will ask experts to answer your questions. Thanks.

0 YC, Tsai over 12 years ago in reply to Raja

Intellectual 590 points

Hi Rajasekaran K,

Thank you for your reply. But the thread you mentioned is not answer me. Now I post the same question on that thread.

in KeyStone devices, the maximum PCIe data payload size is limited to 256 bytes for inbound transactions.

For outbound transfers, the Keystone PCIe peripheral is able to transfer packets of up to 128 bytes.

Is DSPC-8681 maximum PCIe data payload size also limited to 256/128 bytes for Inbound/Outbound transactions?

As far as I knew, DSPC-8681 has PLX PEX8624 PCie Switch which supports maximum payload size 2048 bytes.

Regard.

0 Ralf Goebel over 12 years ago in reply to YC, Tsai

Genius 3715 points

Hi,

since the C6678 DSP is limiting the payload size to 256/128 bytes, you have to uses these values regardless of the switch's capabilities.

Please note that there is a performance problem when a device writes to DSP memory using a payload size of 256 bytes:
http://e2e.ti.com/support/dsp/c6000_multi-core_dsps/f/639/t/158004.aspx

Ralf

0 YC, Tsai over 12 years ago in reply to Ralf Goebel

Intellectual 590 points

Hi Ralf

Thank you for the information.

So the maximum performance for PCIe throughput on DSPC-8681/DSPC-8682 could only be achieved with payload size as 128 bytes, right?

Regards.

0 Ralf Goebel over 12 years ago in reply to YC, Tsai

Genius 3715 points

Yes, I think a maximum payload size of 128 bytes is the best value for the C667x DSP. I'm not sure about different Keystone devices.

Please note that the DSP still can handle inbound read requests with 256 bytes (see DEV_STAT_CTRL register: MAX_REQ_SZ). The request will be compled using multiple smaller packets.

Ralf

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DSPC-8681 PCIe Throughput