According to the measurements for vDPA Live Migration downtime [0], one large source of downtime is the creation of hardware VQs and their associated resources on the devices on the destination VM.
Previous series ([1], [2]) addressed the source part of the Live Migration downtime. This series addresses the destination part: instead of creating hardware VQs and their dependent resources when the device goes into the DRIVER_OK state (which is during downtime), create "blank" VQs at device creation time and only modify them to the received configuration before starting the VQs (DRIVER_OK state). The caveat here is that mlx5_vdpa VQs don't support modifying the VQ size. VQs will be created with a convenient default size and when this size is changed, they will be recreated. The beginning of the series consists of refactorings and preparation. After that, some preparations are made: - Allow creation of "blank" VQs by not configuring them during create_virtqueue() if there are no modified fields. - The VQ Init to Ready state transition is consolidated into the resume_vq(). - Add error handling to suspend/resume code paths. Then VQs are created at device creation time. Finally, the special cases that need full VQ resource recreation are handled. On a 64 CPU, 256 GB VM with 1 vDPA device of 16 VQps, the full VQ resource creation + resume time was ~370ms. Now it's down to 60 ms (only VQ config and resume). The measurements were done on a ConnectX6DX based vDPA device. [0] https://lore.kernel.org/qemu-devel/1701970793-6865-1-git-send-email-si-wei....@oracle.com/ [1] https://lore.kernel.org/lkml/20231018171456.1624030-2-dtatu...@nvidia.com [2] https://lore.kernel.org/lkml/20231219180858.120898-1-dtatu...@nvidia.com --- Changes in v2: - Renamed a function based on v1 review. - Addressed small nits from v1 review. - Added improvement numbers in commit message instead of only cover letter. - Link to v1: https://lore.kernel.org/r/20240617-stage-vdpa-vq-precreate-v1-0-8c0483f0c...@nvidia.com --- Dragos Tatulea (24): vdpa/mlx5: Clarify meaning thorough function rename vdpa/mlx5: Make setup/teardown_vq_resources() symmetrical vdpa/mlx5: Drop redundant code vdpa/mlx5: Drop redundant check in teardown_virtqueues() vdpa/mlx5: Iterate over active VQs during suspend/resume vdpa/mlx5: Remove duplicate suspend code vdpa/mlx5: Initialize and reset device with one queue pair vdpa/mlx5: Clear and reinitialize software VQ data on reset vdpa/mlx5: Rename init_mvqs vdpa/mlx5: Add support for modifying the virtio_version VQ field vdpa/mlx5: Add support for modifying the VQ features field vdpa/mlx5: Set an initial size on the VQ vdpa/mlx5: Start off rqt_size with max VQPs vdpa/mlx5: Set mkey modified flags on all VQs vdpa/mlx5: Allow creation of blank VQs vdpa/mlx5: Accept Init -> Ready VQ transition in resume_vq() vdpa/mlx5: Add error code for suspend/resume VQ vdpa/mlx5: Consolidate all VQ modify to Ready to use resume_vq() vdpa/mlx5: Forward error in suspend/resume device vdpa/mlx5: Use suspend/resume during VQP change vdpa/mlx5: Pre-create hardware VQs at vdpa .dev_add time vdpa/mlx5: Re-create HW VQs under certain conditions vdpa/mlx5: Don't reset VQs more than necessary vdpa/mlx5: Don't enable non-active VQs in .set_vq_ready() drivers/vdpa/mlx5/net/mlx5_vnet.c | 429 +++++++++++++++++++++++++------------ drivers/vdpa/mlx5/net/mlx5_vnet.h | 1 + include/linux/mlx5/mlx5_ifc_vdpa.h | 2 + 3 files changed, 293 insertions(+), 139 deletions(-) --- base-commit: c8fae27d141a32a1624d0d0d5419d94252824498 change-id: 20240617-stage-vdpa-vq-precreate-76df151bed08 Best regards, -- Dragos Tatulea <dtatu...@nvidia.com>
