Adding Robin too.
On Wed, Jul 07, 2021 at 04:55:01PM +0900, David Stevens wrote: > Add support for per-domain dynamic pools of iommu bounce buffers to the > dma-iommu API. This allows iommu mappings to be reused while still > maintaining strict iommu protection. Allocating buffers dynamically > instead of using swiotlb carveouts makes per-domain pools more amenable > on systems with large numbers of devices or where devices are unknown. > > When enabled, all non-direct streaming mappings below a configurable > size will go through bounce buffers. Note that this means drivers which > don't properly use the DMA API (e.g. i915) cannot use an iommu when this > feature is enabled. However, all drivers which work with swiotlb=force > should work. > > Bounce buffers serve as an optimization in situations where interactions > with the iommu are very costly. For example, virtio-iommu operations in > a guest on a linux host require a vmexit, involvement the VMM, and a > VFIO syscall. For relatively small DMA operations, memcpy can be > significantly faster. > > As a performance comparison, on a device with an i5-10210U, I ran fio > with a VFIO passthrough NVMe drive with '--direct=1 --rw=read > --ioengine=libaio --iodepth=64' and block sizes 4k, 16k, 64k, and > 128k. Test throughput increased by 2.8x, 4.7x, 3.6x, and 3.6x. Time > spent in iommu_dma_unmap_(page|sg) per GB processed decreased by 97%, > 94%, 90%, and 87%. Time spent in iommu_dma_map_(page|sg) decreased > by >99%, as bounce buffers don't require syncing here in the read case. > Running with multiple jobs doesn't serve as a useful performance > comparison because virtio-iommu and vfio_iommu_type1 both have big > locks that significantly limit mulithreaded DMA performance. > > This patch set is based on v5.13-rc7 plus the patches at [1]. > > David Stevens (4): > dma-iommu: add kalloc gfp flag to alloc helper > dma-iommu: replace device arguments > dma-iommu: expose a few helper functions to module > dma-iommu: Add iommu bounce buffers to dma-iommu api > > drivers/iommu/Kconfig | 10 + > drivers/iommu/Makefile | 1 + > drivers/iommu/dma-iommu.c | 119 ++++-- > drivers/iommu/io-buffer-pool.c | 656 +++++++++++++++++++++++++++++++++ > drivers/iommu/io-buffer-pool.h | 91 +++++ > include/linux/dma-iommu.h | 12 + > 6 files changed, 861 insertions(+), 28 deletions(-) > create mode 100644 drivers/iommu/io-buffer-pool.c > create mode 100644 drivers/iommu/io-buffer-pool.h > > -- > 2.32.0.93.g670b81a890-goog _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
