Our board is based on Santa Rosa chipset - L7500+GMCH965+ICH8M. The memory is DDR2@333Mhz, DMI x4. We are measuring performance of external PCI-express master on one of ICH8M PCI-e x1 ports. The theoretical read/write performance is 250MB/s. For write we indeed are getting above 200MB/s, but for read we can get approximately 100MB/s. We are osberving that for each 1024 bytes we have delay of 9uS, or, in different mode, for each 128 bytes the delay is 2uS (total read performance in this case is 52MB/s). We are using UEFI BIOS from AMI that uses "Intel Mobile Silicon Support Module" for DMI initialization. Whole the source is in our control. We are suspecting that the problem is in DMI bus utilization - arbitration, priority, latency, etc.
Please help me to improve the read performance on my board.