This patch sets the coherent DMA mask to 64-bit after the be2net driver has been acknowledged that the system is 64-bit DMA capable. The coherent DMA mask is examined by the Intel IOMMU driver to determine whether to allow pass through context mapping for all devices. With this patch, the be2net driver combined with be2net compatible hardware provides comparable performance to the case where vt-d is disabled. The main use case for this change is to decrease the time necessary to copy virtual machine memory during KVM live migration instantiations.
This patch was tested on a system that enables the IOMMU in non-coherent mode. Two DMA remapper issues were encountered and both are in the Intel IOMMU driver with the following patches submitted upstream but not yet commited. Patch 1 - DMAR:[fault reason 02] Present bit in context entry is clear https://lkml.org/lkml/2012/6/15/20 Patch 2 - DMAR:[fault reason 02] Present bit in context entry is clear https://lkml.org/lkml/2011/11/11/279 The performance of this patch was measured with netperf with vt-d enabled and disabled along with kernel boot parameters intel_iommu and iommu. Netperf was run 3 times and averaged for each configuration of vt-d and boot parameters. The command and parameters used in the netperf runs along with results are as follows: # netperf -c -p 12865 -H 10.10.0.2 -t TCP_STREAM -l 60 Recv Send Send Utilization Service Demand Socket Socket Message Elapsed Send Recv Send Recv Size Size Size Time Throughput local remote local remote bytes bytes bytes secs. 10^6bits/s % S % U us/KB us/KB vt-d enabled and intel-iommu=on 87380 16384 16384 60.0 3634.29 16.76 -1.00 2.267 -1.000 vt-d enabled 87380 16384 16384 60.00 6779.01 6.77 -1.00 0.489 -1.000 vt-d disabled 87380 16384 16384 60.00 6807.70 7.00 -1.00 0.505 -1.000 vt-d enabled and intel_iommu=on and iommu=pt 87380 16384 16384 60.00 6849.93 7.19 -1.00 0.516 -1.000 Craig Hada (1): drivers/net: Enable IOMMU pass through for be2net drivers/net/ethernet/emulex/benet/be_main.c | 6 ++++++ 1 files changed, 6 insertions(+), 0 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
