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| /freebsd-10.0-release/sys/dev/bge/ | ||
| H A D | if_bgereg.h | diff 212061 Tue Aug 31 15:45:46 MDT 2010 yongari Split common parent DMA tag into ring DMA tag and TX/RX mbuf DMA tag. All controllers that are not BCM5755 or higher have 4GB boundary DMA bug. Previously bge(4) used 32bit DMA address to workaround the bug(r199670). However this caused the use of bounce buffers such that it resulted in poor performance for systems which have more than 4GB memory. Because bus_dma(9) honors boundary restriction requirement of DMA tag for dynamic buffers, having a separate TX/RX mbuf DMA tag will greatly reduce the possibility of using bounce buffers. For DMA buffers allocated with bus_dmamem_alloc(9), now bge(4) explicitly checks whether the requested memory region crossed the boundary or not. With this change, only the DMA buffer that crossed the boundary will use 32bit DMA address. Other DMA buffers are not affected as separate DMA tag is created for each DMA buffer. Even if 32bit DMA address space is used for a buffer, the chance to use bounce buffer is still very low as the size of buffer is small. This change should eliminate most usage of bounce buffers on systems that have more than 4GB memory. More correct fix would be teaching bus_dma(9) to honor boundary restriction for buffers created with bus_dmamem_alloc(9) but it seems that is not easy. While I'm here cleanup bge_dma_map_addr() and remove unnecessary member variables in bge_dmamap_arg structure. Tested by: marcel |
| H A D | if_bge.c | diff 212061 Tue Aug 31 15:45:46 MDT 2010 yongari Split common parent DMA tag into ring DMA tag and TX/RX mbuf DMA tag. All controllers that are not BCM5755 or higher have 4GB boundary DMA bug. Previously bge(4) used 32bit DMA address to workaround the bug(r199670). However this caused the use of bounce buffers such that it resulted in poor performance for systems which have more than 4GB memory. Because bus_dma(9) honors boundary restriction requirement of DMA tag for dynamic buffers, having a separate TX/RX mbuf DMA tag will greatly reduce the possibility of using bounce buffers. For DMA buffers allocated with bus_dmamem_alloc(9), now bge(4) explicitly checks whether the requested memory region crossed the boundary or not. With this change, only the DMA buffer that crossed the boundary will use 32bit DMA address. Other DMA buffers are not affected as separate DMA tag is created for each DMA buffer. Even if 32bit DMA address space is used for a buffer, the chance to use bounce buffer is still very low as the size of buffer is small. This change should eliminate most usage of bounce buffers on systems that have more than 4GB memory. More correct fix would be teaching bus_dma(9) to honor boundary restriction for buffers created with bus_dmamem_alloc(9) but it seems that is not easy. While I'm here cleanup bge_dma_map_addr() and remove unnecessary member variables in bge_dmamap_arg structure. Tested by: marcel |
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