It is better for a device model to use IOVAs to read/write memory to perform some sort of virtual DMA on behalf of the device. patch 1 exports VFIO group to external user so that it can hold the group reference until finishing using of it. It saves ~500 cycles that are spent on VFIO group looking up, referencing and dereferencing. (this data is measured with 1 VFIO user). patch 2 introduces interface vfio_dma_rw(). patch 3 introduces interfaces vfio_pin_pages_from_group() and vfio_unpin_pages_from_group() to get rid of VFIO group looking-up in vfio_pin_pages() and vfio_unpin_pages(). patch 4-5 let kvmgt switch from calling kvm_read/write_guest() to calling vfio_dma_rw to rw IOVAs. patch 6 let kvmgt switch to use lighter version of vfio_pin/unpin_pages(), i.e. vfio_pin/unpin_pages_from_group() patch 7 enables kvmgt to read/write IOVAs of size larger than PAGE_SIZE. Performance: Comparison between vfio_dma_rw() and kvm_read/write_guest(): 1. avergage CPU cycles of each interface measured with 1 running VM: -------------------------------------------------- | rw | avg cycles of | | size | (vfio_dma_rw - kvm_read/write_guest) | |---------- ---------------------------------------| | <= 1 page | +155 ~ +195 | |--------------------------------------------------| | 5 pages | -530 | |--------------------------------------------------| | 20 pages | -2005 ~ -2533 | -------------------------------------------------- 2. average scores base: base code before applying code in this series. use kvm_read/write_pages() to rw IOVAs base + this series: use vfio_dma_rw() to read IOVAs and use vfio_pin/unpin_pages_from_group(), and kvmgt is able to rw several pages at a time. Scores of benchmarks running in 1 VM each: ----------------------------------------------------------------- | | glmark2 | lightsmark | openarena | heavens | |-----------------------------------------------------------------| | base | 1248 | 219.70 | 114.9 | 560 | |-----------------------------------------------------------------| |base + this series | 1248 | 225.8 | 115 | 559 | ----------------------------------------------------------------- Sum of scores of two benchmark instances running in 2 VMs each: ------------------------------------------------------- | | glmark2 | lightsmark | openarena | |-------------------------------------------------------| | base | 812 | 211.46 | 115.3 | |-------------------------------------------------------| |base + this series | 814 | 214.69 | 115.9 | ------------------------------------------------------- Changelogs: v2 --> v3: - add vfio_group_get_external_user_from_dev() to improve performance (Alex) - add vfio_pin/unpin_pages_from_group() to avoid repeated looking up of VFIO group in vfio_pin/unpin_pages() (Alex) - add a check for IOMMU_READ permission. (Alex) - rename vfio_iommu_type1_rw_dma_nopin() to vfio_iommu_type1_dma_rw_chunk(). (Alex) - in kvmgt, change "write ? vfio_dma_rw(...,true) : vfio_dma_rw(...,false)" to vfio_dma_rw(dev, gpa, buf, len, write) (Alex and Paolo) - in kvmgt, instead of read/write context pages 1:1, combining the reads/writes of continuous IOVAs to take advantage of vfio_dma_rw() for faster crossing page boundary accesses. v1 --> v2: - rename vfio_iova_rw to vfio_dma_rw, vfio iommu driver ops .iova_rw to .dma_rw. (Alex). - change iova and len from unsigned long to dma_addr_t and size_t, respectively. (Alex) - fix possible overflow in dma->vaddr + iova - dma->iova + offset (Alex) - split DMAs from on page boundary to on max available size to eliminate redundant searching of vfio_dma and switching mm. (Alex) - add a check for IOMMU_WRITE permission. Yan Zhao (7): vfio: allow external user to get vfio group from device vfio: introduce vfio_dma_rw to read/write a range of IOVAs vfio: avoid inefficient lookup of VFIO group in vfio_pin/unpin_pages drm/i915/gvt: hold reference of VFIO group during opening of vgpu drm/i915/gvt: subsitute kvm_read/write_guest with vfio_dma_rw drm/i915/gvt: avoid unnecessary lookup in each vfio pin & unpin pages drm/i915/gvt: rw more pages a time for shadow context drivers/gpu/drm/i915/gvt/gvt.h | 1 + drivers/gpu/drm/i915/gvt/kvmgt.c | 43 +++---- drivers/gpu/drm/i915/gvt/scheduler.c | 101 +++++++++++----- drivers/vfio/vfio.c | 175 +++++++++++++++++++++++++++ drivers/vfio/vfio_iommu_type1.c | 77 ++++++++++++ include/linux/vfio.h | 13 ++ 6 files changed, 358 insertions(+), 52 deletions(-) -- 2.17.1
