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: Anton Blanchard <anton@samba.org>
Cc: Akinobu Mita <akinobu.mita@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
e269b08517