• Vincent Whitchurch's avatar
    ARM: 8812/1: Optimise copy_{from/to}_user for !CPU_USE_DOMAINS · f441882a
    Vincent Whitchurch authored
    ARMv6+ processors do not use CONFIG_CPU_USE_DOMAINS and use privileged
    ldr/str instructions in copy_{from/to}_user.  They are currently
    unnecessarily using single ldr/str instructions and can use ldm/stm
    instructions instead like memcpy does (but with appropriate fixup
    tables).
    
    This speeds up a "dd if=foo of=bar bs=32k" on a tmpfs filesystem by
    about 4% on my Cortex-A9.
    
    before:134217728 bytes (128.0MB) copied, 0.543848 seconds, 235.4MB/s
    before:134217728 bytes (128.0MB) copied, 0.538610 seconds, 237.6MB/s
    before:134217728 bytes (128.0MB) copied, 0.544356 seconds, 235.1MB/s
    before:134217728 bytes (128.0MB) copied, 0.544364 seconds, 235.1MB/s
    before:134217728 bytes (128.0MB) copied, 0.537130 seconds, 238.3MB/s
    before:134217728 bytes (128.0MB) copied, 0.533443 seconds, 240.0MB/s
    before:134217728 bytes (128.0MB) copied, 0.545691 seconds, 234.6MB/s
    before:134217728 bytes (128.0MB) copied, 0.534695 seconds, 239.4MB/s
    before:134217728 bytes (128.0MB) copied, 0.540561 seconds, 236.8MB/s
    before:134217728 bytes (128.0MB) copied, 0.541025 seconds, 236.6MB/s
    
     after:134217728 bytes (128.0MB) copied, 0.520445 seconds, 245.9MB/s
     after:134217728 bytes (128.0MB) copied, 0.527846 seconds, 242.5MB/s
     after:134217728 bytes (128.0MB) copied, 0.519510 seconds, 246.4MB/s
     after:134217728 bytes (128.0MB) copied, 0.527231 seconds, 242.8MB/s
     after:134217728 bytes (128.0MB) copied, 0.525030 seconds, 243.8MB/s
     after:134217728 bytes (128.0MB) copied, 0.524236 seconds, 244.2MB/s
     after:134217728 bytes (128.0MB) copied, 0.523659 seconds, 244.4MB/s
     after:134217728 bytes (128.0MB) copied, 0.525018 seconds, 243.8MB/s
     after:134217728 bytes (128.0MB) copied, 0.519249 seconds, 246.5MB/s
     after:134217728 bytes (128.0MB) copied, 0.518527 seconds, 246.9MB/s
    Reviewed-by: default avatarNicolas Pitre <nico@linaro.org>
    Signed-off-by: default avatarVincent Whitchurch <vincent.whitchurch@axis.com>
    Signed-off-by: default avatarRussell King <rmk+kernel@armlinux.org.uk>
    f441882a
copy_to_user.S 2.57 KB