• Anton Blanchard's avatar
    iommu: inline iommu_num_pages · e269b085
    Anton Blanchard authored
    A profile of a network benchmark showed iommu_num_pages rather high up:
    
         0.52%  iommu_num_pages
    
    Looking at the profile, an integer divide is taking almost all of the time:
    
          %
             :      c000000000376ea4 <.iommu_num_pages>:
        1.93 :      c000000000376ea4:       fb e1 ff f8     std     r31,-8(r1)
        0.00 :      c000000000376ea8:       f8 21 ff c1     stdu    r1,-64(r1)
        0.00 :      c000000000376eac:       7c 3f 0b 78     mr      r31,r1
        3.86 :      c000000000376eb0:       38 84 ff ff     addi    r4,r4,-1
        0.00 :      c000000000376eb4:       38 05 ff ff     addi    r0,r5,-1
        0.00 :      c000000000376eb8:       7c 84 2a 14     add     r4,r4,r5
       46.95 :      c000000000376ebc:       7c 00 18 38     and     r0,r0,r3
       45.66 :      c000000000376ec0:       7c 84 02 14     add     r4,r4,r0
        0.00 :      c000000000376ec4:       7c 64 2b 92     divdu   r3,r4,r5
        0.00 :      c000000000376ec8:       38 3f 00 40     addi    r1,r31,64
        0.00 :      c000000000376ecc:       eb e1 ff f8     ld      r31,-8(r1)
        1.61 :      c000000000376ed0:       4e 80 00 20     blr
    
    Since every caller of iommu_num_pages passes in a constant power of two
    we can inline this such that the divide is replaced by a shift. The
    entire function is only a few instructions once optimised, so it is
    a good candidate for inlining overall.
    Signed-off-by: 's avatarAnton Blanchard <anton@samba.org>
    Cc: Akinobu Mita <akinobu.mita@gmail.com>
    Signed-off-by: 's avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: 's avatarLinus Torvalds <torvalds@linux-foundation.org>
    e269b085
iommu-helper.h 911 Bytes