On Jan 29, 2008 11:10 AM, Haavard Skinnemoen <[EMAIL PROTECTED]> wrote: [..] > The dmatest client shows no problems, but the performance is not as > good as it should be yet -- iperf shows a slight slowdown when > enabling TCP receive copy offload. This is probably because the > controller is set up to always do byte transfers; I'll try to optimize > this, but if someone can tell me if there any guaranteed alignment > requirements for the users of the DMA engine API, that would help a > lot. >
dmaengine punts to the dma-mapping api. So no, there are no alignment guarantees. The performance loss is probably more related to the cache synchronization overkill of get_user_pages(). I/O incoherent architectures end up synchronizing entire pages when we only need to sync a kilobyte or two in this path. -- Dan -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/