Huang, Shane wrote: > Hi Tejun, > >> -----Original Message----- >> From: Tejun Heo [mailto:htejun@xxxxxxxxx] >>> ahci 0000:00:12.0: version 3.0_ >>> ahci 0000:00:12.0: PCI INT A -> GSI 22 (level, low) -> IRQ 22 >>> ahci 0000:00:12.0: Fujitsu-Siemens AMILO Pa 2510: this >> board can't do 64bit >>> DMA, forcing 32bit >>> ahci 0000:00:12.0: controller can't do 64bit DMA, forcing 32bit >>> ahci 0000:00:12.0: AHCI 0001.0100 32 slots 4 ports 3 Gbps >> 0xf impl SATA mode >>> ahci 0000:00:12.0: flags: ncq sntf ilck pm led clo pmp pio slum part >>> It's correct now. >> Cool, patch posted with the id string shortened. > > Just some small questions about this topic: > > What is the actual impact of 64-bit DMA not being available? If IO happens to memory above 4G it will either be bounced (ie. DMA will be performed to a bounce buffer < 4G which is copied from / to the original buffer or more likely iommu will kick in. > How important is it to have this enabled? > > In other words, will the performance be improved significantly > after it is enabled? Do you have any experimental data for it? :-) There probably won't be any noticeable performance regression if iommu is working properly and no, I don't have any concrete numbers. Thanks.. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
