No change in behavior observed from v1 on my config (DGX H100). Thanks! Reviewed-by: "Mitchell Augustin" <mitchell.augustin@xxxxxxxxxxxxx> Tested-by: "Mitchell Augustin" <mitchell.augustin@xxxxxxxxxxxxx> On Tue, Feb 18, 2025 at 4:22 PM Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > > v2: > - Rewrapped comment block in 3/6 > - Added 4/6 to use consistent types (Jason) > - Renamed s/pgmask/addr_mask/ (David) > - Updated 6/6 with proposed epfn algorithm (Jason) > - Applied and retained sign-offs for all but 6/6 where the epfn > calculation changed > > v1: https://lore.kernel.org/all/20250205231728.2527186-1-alex.williamson@xxxxxxxxxx/ > > As GPU BAR sizes increase, the overhead of DMA mapping pfnmap ranges has > become a significant overhead for VMs making use of device assignment. > Not only does each mapping require upwards of a few seconds, but BARs > are mapped in and out of the VM address space multiple times during > guest boot. Also factor in that multi-GPU configurations are > increasingly commonplace and BAR sizes are continuing to increase. > Configurations today can already be delayed minutes during guest boot. > > We've taken steps to make Linux a better guest by batching PCI BAR > sizing operations[1], but it only provides and incremental improvement. > > This series attempts to fully address the issue by leveraging the huge > pfnmap support added in v6.12. When we insert pfnmaps using pud and pmd > mappings, we can later take advantage of the knowledge of the mapping > level page mask to iterate on the relevant mapping stride. In the > commonly achieved optimal case, this results in a reduction of pfn > lookups by a factor of 256k. For a local test system, an overhead of > ~1s for DMA mapping a 32GB PCI BAR is reduced to sub-millisecond (8M > page sized operations reduced to 32 pud sized operations). > > Please review, test, and provide feedback. I hope that mm folks can > ack the trivial follow_pfnmap_args update to provide the mapping level > page mask. Naming is hard, so any preference other than pgmask is > welcome. Thanks, > > Alex > > [1]https://lore.kernel.org/all/20250120182202.1878581-1-alex.williamson@xxxxxxxxxx/ > > > Alex Williamson (6): > vfio/type1: Catch zero from pin_user_pages_remote() > vfio/type1: Convert all vaddr_get_pfns() callers to use vfio_batch > vfio/type1: Use vfio_batch for vaddr_get_pfns() > vfio/type1: Use consistent types for page counts > mm: Provide address mask in struct follow_pfnmap_args > vfio/type1: Use mapping page mask for pfnmaps > > drivers/vfio/vfio_iommu_type1.c | 123 ++++++++++++++++++++------------ > include/linux/mm.h | 2 + > mm/memory.c | 1 + > 3 files changed, 80 insertions(+), 46 deletions(-) > > -- > 2.48.1 > -- Mitchell Augustin Software Engineer - Ubuntu Partner Engineering Email:mitchell.augustin@xxxxxxxxxxxxx Location:United States of America canonical.com ubuntu.com
