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With the conversion to drm_gpuvm, we lost the lazy VMA cleanup, which means that fb cleanup/unpin when pageflipping to new scanout buffers immediately unmaps the scanout buffer. This is costly (with tlbinv, it can be 4-6ms for a 1080p scanout buffer, and more for higher resolutions)! To avoid this, introduce a vma_ref, which is incremented whenever userspace has a GEM handle or dma-buf fd. When unpinning if the vm is the kms->vm we defer tearing down the VMA until the vma_ref drops to zero. If the buffer is still part of a flip-chain then userspace will be holding some sort of reference to the BO, either via a GEM handle and/or dma-buf fd. So this avoids unmapping the VMA when there is a strong possibility that it will be needed again. Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com> Tested-by: Antonino Maniscalco <antomani103@gmail.com> Reviewed-by: Antonino Maniscalco <antomani103@gmail.com> Patchwork: https://patchwork.freedesktop.org/patch/661538/
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.