• Nicholas Piggin's avatar
    powerpc/64s: Improve RFI L1-D cache flush fallback · bdcb1aef
    Nicholas Piggin authored
    The fallback RFI flush is used when firmware does not provide a way
    to flush the cache. It's a "displacement flush" that evicts useful
    data by displacing it with an uninteresting buffer.
    
    The flush has to take care to work with implementation specific cache
    replacment policies, so the recipe has been in flux. The initial
    slow but conservative approach is to touch all lines of a congruence
    class, with dependencies between each load. It has since been
    determined that a linear pattern of loads without dependencies is
    sufficient, and is significantly faster.
    
    Measuring the speed of a null syscall with RFI fallback flush enabled
    gives the relative improvement:
    
    P8 - 1.83x
    P9 - 1.75x
    
    The flush also becomes simpler and more adaptable to different cache
    geometries.
    Signed-off-by: default avatarNicholas Piggin <npiggin@gmail.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    bdcb1aef
exceptions-64s.S 52.8 KB