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When an egress resource(SDMA descriptors, pio credits) is not available, a sending thread will be put on the resource's wait queue. When the resource becomes available again, up to a fixed number of sending threads can be awakened sequentially and removed from the wait queue, depending on the number of waiting threads and the number of free resources. Since each awakened sending thread will send as many packets as possible, it is highly likely that the first sending thread will consume all the egress resources. Subsequently, it will be put back to the end of the wait queue. Depending on the timing when the later sending threads wake up, they may not be able to send any packet and be again put back to the end of the wait queue sequentially, right behind the first sending thread. This starvation cycle continues until some sending threads exceed their retry limit and consequently fail. This patch fixes the issue by two simple approaches: (1) Any starved sending thread will be put to the head of the wait queue while a served sending thread will be put to the tail; (2) The most starved sending thread will be served first. Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com> Signed-off-by: Kaike Wan <kaike.wan@intel.com> Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com> Signed-off-by: Doug Ledford <dledford@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.