OS X Intel DMA speed issues

Hi,

 

The company I work for produces a series of PCI interface cards for imagesetters and we have PCI drivers and support software for both Mac OS X and PC. Some recent testing as part of porting to OS X Intel has revealed a major disparity in terms of maximum data rates between PC and OS X Intel.

 

Speed tests indicate that on a PC we can achieve approx 26Mb/sec which is more than sufficient for the engines we drive.

The same test on Mac OS X PPC generated results of approx 10Mb/sec which, while fast enough for our needs, is still approximately 1/3 the speed of the PC.

The same test on Mac OS X Intel generated results of approx 2Mb/sec which is nowhere near fast enough to drive even some of the slower engines. Timestamps from the driver indicate that it takes approx 400ms to transfer 939000 bytes from Mac memory to on-board memory.

 

Analysing the PCIe bus behaviour, we noticed that we were experiencing multiple retries followed by a 'disconnect with data' when trying to read the data from the Mac memory.

This does transfer data but at a very slow rate (see above).

 

Our interface card uses a PLX9056 chip connected via a PCIexpress bridge to perform the DMA.

 

Are there any known issues with DMA'ing data from Mac memory to memory onboard a PCIe card?

Any ideas as to why I am getting such terrible data rates?

 

Peter Young

 

 

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