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authorIlya Dryomov <idryomov@gmail.com>2016-09-27 12:30:09 +0200
committerIlya Dryomov <idryomov@gmail.com>2016-10-05 23:02:04 +0200
commit74a5293832b3c1f7cb8f86fb9af9ee747138d355 (patch)
tree428a431d62ee601f6dd3ed5b0426714d38c7c66b /net
parent464691bd52b46a565153ec2a3b8b9984dacd4a00 (diff)
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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.c12
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;