On Tue, Jun 26, 2007 at 05:56:49PM +0200, Andi Kleen wrote: > > > - The IOMMU can merge sg lists into a single virtual block. This could > > > potentially speed up SG IO when the device is slow walking SG > > > lists. [I long ago benchmarked 5% on some block benchmark with > > > an old MPT Fusion; but it probably depends a lot on the HBA] > > > > But most devices are SG-capable. > > Your point being?
That the fact that an IOMMU can do SG for non-SG-capble cards is not interesting from a "reason for inclusion" POV. > > How much? we have numbers (to be presented at OLS later this week) > > that show that on bare-metal an IOMMU can cost as much as 15%-30% > > more CPU utilization for an IO intensive workload (netperf). It > > will be interesting to see comparable numbers for VT-d. > > That is something that needs more work. Yup. I'm working on it (mostly in the context of Calgary) but also looking at improvements to the DMA-API interface and usage. > We should probably have a switch to use the IOMMU only for specific > devices (e.g. for the KVM case) r only when remapping is > needed. Calgary already does this internally (via calgary=disable=<BUSNUM>) but that's pretty ugly. It would be better to do it in a generic fashion when deciding which dma_ops to call (i.e., a dma_ops per bus or device). > Also the user interface for X server case needs more work. Is anyone working on it? Cheers, Muli - 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/
