• Mark Brown's avatar
    arm64: topology: Fix handling of multi-level cluster MPIDR-based detection · 1cefdaea
    Mark Brown authored
    The only requirement the scheduler has on cluster IDs is that they must
    be unique.  When enumerating the topology based on MPIDR information the
    kernel currently generates cluster IDs by using the first level of
    affinity above the core ID (either level one or two depending on if the
    core has multiple threads) however the ARMv8 architecture allows for up
    to three levels of affinity.  This means that an ARMv8 system may
    contain cores which have MPIDRs identical other than affinity level
    three which with current code will cause us to report multiple cores
    with the same identification to the scheduler in violation of its
    uniqueness requirement.
    
    Ensure that we do not violate the scheduler requirements on systems that
    uses all the affinity levels by incorporating both affinity levels two
    and three into the cluser ID when the cores are not threaded.
    
    While no currently known hardware uses multi-level clusters it is better
    to program defensively, this will help ease bringup of systems that have
    them and will ensure that things like distribution install media do not
    need to be respun to replace kernels in order to deploy such systems.
    In the worst case the system will work but perform suboptimally until a
    kernel modified to handle the new topology better is installed, in the
    best case this will be an adequate description of such topologies for
    the scheduler to perform well.
    Signed-off-by: default avatarMark Brown <broonie@linaro.org>
    Signed-off-by: default avatarWill Deacon <will.deacon@arm.com>
    1cefdaea
topology.c 6.64 KB