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| author | Ilya Dryomov <idryomov@gmail.com> | 2016-09-27 12:30:09 +0200 |
|---|---|---|
| committer | Ilya Dryomov <idryomov@gmail.com> | 2016-10-05 23:02:04 +0200 |
| commit | 74a5293832b3c1f7cb8f86fb9af9ee747138d355 (patch) | |
| tree | 428a431d62ee601f6dd3ed5b0426714d38c7c66b /net | |
| parent | 464691bd52b46a565153ec2a3b8b9984dacd4a00 (diff) | |
| download | linux-74a5293832b3c1f7cb8f86fb9af9ee747138d355.tar.gz linux-74a5293832b3c1f7cb8f86fb9af9ee747138d355.tar.bz2 linux-74a5293832b3c1f7cb8f86fb9af9ee747138d355.zip | |
crush: don't normalize input of crush_ln iteratively
Use __builtin_clz() supported by GCC and Clang to figure out
how many bits we should shift instead of shifting by a bit
in a loop until the value gets normalized. Improves performance
of this function by up to 3x in worst-case scenario and overall
straw2 performance by ~10%.
Reflects ceph.git commit 110de33ca497d94fc4737e5154d3fe781fa84a0a.
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Diffstat (limited to 'net')
| -rw-r--r-- | net/ceph/crush/mapper.c | 12 |
1 files changed, 9 insertions, 3 deletions
diff --git a/net/ceph/crush/mapper.c b/net/ceph/crush/mapper.c index 5fcfb98f309e..511ade95339a 100644 --- a/net/ceph/crush/mapper.c +++ b/net/ceph/crush/mapper.c @@ -253,9 +253,15 @@ static __u64 crush_ln(unsigned int xin) /* normalize input */ iexpon = 15; - while (!(x & 0x18000)) { - x <<= 1; - iexpon--; + + /* + * figure out number of bits we need to shift and + * do it in one step instead of iteratively + */ + if (!(x & 0x18000)) { + int bits = __builtin_clz(x & 0x1FFFF) - 16; + x <<= bits; + iexpon = 15 - bits; } index1 = (x >> 8) << 1; |