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Currently, hardware VQs are created right when the vdpa device gets into DRIVER_OK state. That is easier because most of the VQ state is known by then. This patch switches to creating all VQs and their associated resources at device creation time. The motivation is to reduce the vdpa device live migration downtime by moving the expensive operation of creating all the hardware VQs and their associated resources out of downtime on the destination VM. The VQs are now created in a blank state. The VQ configuration will happen later, on DRIVER_OK. Then the configuration will be applied when the VQs are moved to the Ready state. When .set_vq_ready() is called on a VQ before DRIVER_OK, special care is needed: now that the VQ is already created a resume_vq() will be triggered too early when no mr has been configured yet. Skip calling resume_vq() in this case, let it be handled during DRIVER_OK. For virtio-vdpa, the device configuration is done earlier during .vdpa_dev_add() by vdpa_register_device(). Avoid calling setup_vq_resources() a second time in that case. 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. Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com> Reviewed-by: Cosmin Ratiu <cratiu@nvidia.com> Message-Id: <20240626-stage-vdpa-vq-precreate-v2-21-560c491078df@nvidia.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.