PCIe throughput performances

Youssef Lyoussfi

Hi,

I measured PCIe throughput performances between two C6678 and i found results thar are similar to the throughput performances making by TI in the document "Throughput Performance Guide for C66x KeyStone Devices".

According to PCIe specifications, memory read transactions are non-posted and memory write are posted, so it seems that memory write performances are better than memory read, byt according to my and TI results, it's said the opposit.

Anyone have an idea why memory read is better than memory write in PCIe ?

Sincerly

Youssef

over 13 years ago

0 Steven Ji over 13 years ago

TI__Genius 12065 points

Youssef,

The Performance Guide has two columns for the PCIe throughput: 64byte payload size and 128byte payload size.

In 64B case, the memory write and read performance are very similar, and actually Write is a little better than Read.

In 128B case, because there are some overhead introduced by the bridge inside the device for PCIe memory write, the Write performance has some degradation comparing to the memory Read. We showed the actual throughput we could get in the device in the Performance Guide which may match your observation as well.

So what you have measured should be correct that, with 128B payload size, memory Read performance is better than memory Write for PCIe.

0 Youssef Lyoussfi over 13 years ago in reply to Steven Ji

Intellectual 390 points

Thanks Steven for reply,

I don't inderstand which bridge you speak about that can add an overhead just for memory write,

I need more explanation please.

Best regards,

Youssef

0 Steven Ji over 13 years ago in reply to Youssef Lyoussfi

TI__Genius 12065 points

Youssef,

I think it is the interface bridge between PCIe port and external bus. Unfortunately, it is not configurable.

So hope the current Write performance could still satisfy your application.

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PCIe throughput performances