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Reading TX queue indexes from the device memory on each interrupt is expensive. It's doubly expensive with XDP running since we have two TX rings to check there. If the software indexes indicate that the TX queue is completely empty, however, we don't need to look at the device completion index at all. The queuing CPU is doing a wmb() before kicking the device TX so we should be safe to assume on the CPU handling the completions will never see old value of the software copy of the index. Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com> Signed-off-by: David S. Miller <davem@davemloft.net>
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.