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When we don't have the DirectLPI feature, we must work around the architecture shortcomings to be able to perform the required maintenance (interrupt masking, clearing and injection). For this, we create a fake device whose sole purpose is to provide a way to issue commands as if we were dealing with LPIs coming from that device (while they actually originate from the ITS). This fake device doesn't have LPIs allocated to it, but instead uses the VPE LPIs. Of course, this could be a real bottleneck, and a naive implementation would require 6 commands to issue an invalidation. Instead, let's allocate at least one event per physical CPU (rounded up to the next power of 2), and opportunistically map the VPE doorbell to an event. This doorbell will be mapped until we roll over and need to reallocate this slot. This ensures that most of the time, we only need 2 commands to issue an INV, INT or CLEAR, making the performance a lot better, given that we always issue a CLEAR on entry, and an INV on each side of a trapped WFI. Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
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.