• Rob Herring's avatar
    ARM: 7587/1: implement optimized percpu variable access · 14318efb
    Rob Herring authored
    Use the previously unused TPIDRPRW register to store percpu offsets.
    TPIDRPRW is only accessible in PL1, so it can only be used in the kernel.
    
    This replaces 2 loads with a mrc instruction for each percpu variable
    access. With hackbench, the performance improvement is 1.4% on Cortex-A9
    (highbank). Taking an average of 30 runs of "hackbench -l 1000" yields:
    
    Before: 6.2191
    After: 6.1348
    
    Will Deacon reported similar delta on v6 with 11MPCore.
    
    The asm "memory clobber" are needed here to ensure the percpu offset
    gets reloaded. Testing by Will found that this would not happen in
    __schedule() which is a bit of a special case as preemption is disabled
    but the execution can move cores.
    Signed-off-by: default avatarRob Herring <rob.herring@calxeda.com>
    Acked-by: default avatarWill Deacon <will.deacon@arm.com>
    Acked-by: default avatarNicolas Pitre <nico@linaro.org>
    Signed-off-by: default avatarRussell King <rmk+kernel@arm.linux.org.uk>
    14318efb
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