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The only times the nil-parent (root node) condition is true is when the node is the first in the tree, or after fixing rbtree rule #4 and the case 1 rebalancing made the node the root. Such conditions do not apply most of the time: (i) The common case in an rbtree is to have more than a single node, so this is only true for the first rb_insert(). (ii) While there is a chance only one first rotation is needed, cases where the node's uncle is black (cases 2,3) are more common as we can have the following scenarios during the rotation looping: case1 only, case1+1, case2+3, case1+2+3, case3 only, etc. This patch, therefore, adds an unlikely() optimization to this conditional. When profiling with CONFIG_PROFILE_ANNOTATED_BRANCHES, a kernel build shows that the incorrect rate is less than 15%, and for workloads that involve insert mostly trees overtime tend to have less than 2% incorrect rate. Link: http://lkml.kernel.org/r/20170719014603.19029-3-dave@stgolabs.net Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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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.