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Dma-bufs should already be device coherent, as they are only pulled in the CPU domain via the begin/end cpu_access calls. As we cache the mapping set up by dma_map_sg a CPU sync at this point will not actually guarantee proper coherency on non-coherent architectures, so we can as well stop pretending. This is an important performance fix for architectures which need explicit cache synchronization and userspace doing lots of dma-buf imports. Improves Weston on Etnaviv performance 5x, where before this patch > 90% of Weston CPU time was spent synchronizing caches for buffers which are already device coherent. Signed-off-by: Lucas Stach <l.stach@pengutronix.de> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch> Link: https://patchwork.freedesktop.org/patch/msgid/20171130173428.8666-1-l.stach@pengutronix.de
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.