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The sloppy nature of lockless access to percpu pointers (s->current_path) in rr_select_path(), from multiple threads, is causing some paths to used more than others -- which results in less IO performance being observed. Revert these upstream commits to restore truly symmetric round-robin IO submission in DM multipath:b0b477cdm round robin: use percpu 'repeat_count' and 'current_path'802934bdm round robin: do not use this_cpu_ptr() without having preemption disabled There is no benefit to all this complexity if repeat_count = 1 (which is the recommended default). Cc: stable@vger.kernel.org # 4.6+ Signed-off-by: Mike Snitzer <snitzer@redhat.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.