mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
synced 2026-05-14 04:09:18 -04:00
d334a5637d
As newer, higher speed devices are developed, perf data shows that the amount of MMIO that is performed when submitting commands to the IOMMU causes performance issues. Currently, the command submission path reads the command buffer head and tail pointers and then writes the tail pointer once the command is ready. The tail pointer is only ever updated by the driver so it can be tracked by the driver without having to read it from the hardware. The head pointer is updated by the hardware, but can be read opportunistically. Reading the head pointer only when it appears that there might not be room in the command buffer and then re-checking the available space reduces the number of times the head pointer has to be read. Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> Signed-off-by: Joerg Roedel <jroedel@suse.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.