Are there known performance issues with some system controllers PCI interfaces?
A. Yes, there is a known issue with a Discovery1 system controller affecting transmit dma on boards with PowerPC 74xx processors. During transmit DMA burst reads from SDRAM initiated by a bus-master, the Discovery1 target may disconnect frequently and prematurely (after one 32-byte cache line is transferred) while snooping the cache and/or fetching data from SDRAM. This results in excessive retries and poor transmit DMA performance (85MB/sec or less even with 64-bit/66 MHZ PCI). It also may cause excessive transmit latency further inhibiting driver and protocol stack performance. Flushing and invalidating the cache in the driver during transmit (normally not necessary with hardware cache coherency) helps to minimize the impact of this problem, however transmit DMA performance may be still constrained on systems utilizing this controller.
Related Questions
- Does the DragonBall EZ have a DRAM controller and does it have the ability to improve system performance assuming you use the right DRAM?
- Is the use of 32 bit PCI addressing a performance limitation in this system? Does using 64 bit PCI addressing increase performance?
- Are there known performance issues with some system controllers PCI interfaces?
