Fork of alistair23 Linux kernel for reMarkable from https://github.com/alistair23/linux
be664cbefc
Currently, when setting up the IRQ for a q_vector, we set an affinity hint based on the v_idx of that q_vector. Meaning a loop iterates on v_idx, which is an incremental value, and the cpumask is created based on this value. This is a problem in systems with multiple logical CPUs per core (like in simultaneous multithreading (SMT) scenarios). If we disable some logical CPUs, by turning SMT off for example, we will end up with a sparse cpu_online_mask, i.e., only the first CPU in a core is online, and incremental filling in q_vector cpumask might lead to multiple offline CPUs being assigned to q_vectors. Example: if we have a system with 8 cores each one containing 8 logical CPUs (SMT == 8 in this case), we have 64 CPUs in total. But if SMT is disabled, only the 1st CPU in each core remains online, so the cpu_online_mask in this case would have only 8 bits set, in a sparse way. In general case, when SMT is off the cpu_online_mask has only C bits set: 0, 1*N, 2*N, ..., C*(N-1) where C == # of cores; N == # of logical CPUs per core. In our example, only bits 0, 8, 16, 24, 32, 40, 48, 56 would be set. Instead, we should only assign hints for CPUs which are online. Even better, the kernel already provides a function, cpumask_local_spread() which takes an index and returns a CPU, spreading the interrupts across local NUMA nodes first, and then remote ones if necessary. Since we generally have a 1:1 mapping between vectors and CPUs, there is no real advantage to spreading vectors to local CPUs first. In order to avoid mismatch of the default XPS hints, we'll pass -1 so that it spreads across all CPUs without regard to the node locality. Note that we don't need to change the q_vector->affinity_mask as this is initialized to cpu_possible_mask, until an actual affinity is set and then notified back to us. Signed-off-by: Jacob Keller <jacob.e.keller@intel.com> Tested-by: Andrew Bowers <andrewx.bowers@intel.com> Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com> |
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README
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.