diff options
Diffstat (limited to 'net/ceph/crush/mapper.c')
| -rw-r--r-- | net/ceph/crush/mapper.c | 101 |
1 files changed, 101 insertions, 0 deletions
diff --git a/net/ceph/crush/mapper.c b/net/ceph/crush/mapper.c index 91c41fe83113..5b47736d27d9 100644 --- a/net/ceph/crush/mapper.c +++ b/net/ceph/crush/mapper.c @@ -20,6 +20,7 @@ #include <linux/crush/crush.h> #include <linux/crush/hash.h> +#include "crush_ln_table.h" /* * Implement the core CRUSH mapping algorithm. @@ -237,6 +238,102 @@ static int bucket_straw_choose(struct crush_bucket_straw *bucket, return bucket->h.items[high]; } +// compute 2^44*log2(input+1) +uint64_t crush_ln(unsigned xin) +{ + unsigned x=xin, x1; + int iexpon, index1, index2; + uint64_t RH, LH, LL, xl64, result; + + x++; + + // normalize input + iexpon = 15; + while(!(x&0x18000)) { x<<=1; iexpon--; } + + index1 = (x>>8)<<1; + // RH ~ 2^56/index1 + RH = __RH_LH_tbl[index1 - 256]; + // LH ~ 2^48 * log2(index1/256) + LH = __RH_LH_tbl[index1 + 1 - 256]; + + // RH*x ~ 2^48 * (2^15 + xf), xf<2^8 + xl64 = (int64_t)x * RH; + xl64 >>= 48; + x1 = xl64; + + result = iexpon; + result <<= (12 + 32); + + index2 = x1 & 0xff; + // LL ~ 2^48*log2(1.0+index2/2^15) + LL = __LL_tbl[index2]; + + LH = LH + LL; + + LH >>= (48-12 - 32); + result += LH; + + return result; +} + + +/* + * straw2 + * + * for reference, see: + * + * http://en.wikipedia.org/wiki/Exponential_distribution#Distribution_of_the_minimum_of_exponential_random_variables + * + */ + +static int bucket_straw2_choose(struct crush_bucket_straw2 *bucket, + int x, int r) +{ + unsigned i, high = 0; + unsigned u; + unsigned w; + __s64 ln, draw, high_draw = 0; + + for (i = 0; i < bucket->h.size; i++) { + w = bucket->item_weights[i]; + if (w) { + u = crush_hash32_3(bucket->h.hash, x, + bucket->h.items[i], r); + u &= 0xffff; + + /* + * for some reason slightly less than 0x10000 produces + * a slightly more accurate distribution... probably a + * rounding effect. + * + * the natural log lookup table maps [0,0xffff] + * (corresponding to real numbers [1/0x10000, 1] to + * [0, 0xffffffffffff] (corresponding to real numbers + * [-11.090355,0]). + */ + ln = crush_ln(u) - 0x1000000000000ll; + + /* + * divide by 16.16 fixed-point weight. note + * that the ln value is negative, so a larger + * weight means a larger (less negative) value + * for draw. + */ + draw = div64_s64(ln, w); + } else { + draw = S64_MIN; + } + + if (i == 0 || draw > high_draw) { + high = i; + high_draw = draw; + } + } + return bucket->h.items[high]; +} + + static int crush_bucket_choose(struct crush_bucket *in, int x, int r) { dprintk(" crush_bucket_choose %d x=%d r=%d\n", in->id, x, r); @@ -254,12 +351,16 @@ static int crush_bucket_choose(struct crush_bucket *in, int x, int r) case CRUSH_BUCKET_STRAW: return bucket_straw_choose((struct crush_bucket_straw *)in, x, r); + case CRUSH_BUCKET_STRAW2: + return bucket_straw2_choose((struct crush_bucket_straw2 *)in, + x, r); default: dprintk("unknown bucket %d alg %d\n", in->id, in->alg); return in->items[0]; } } + /* * true if device is marked "out" (failed, fully offloaded) * of the cluster |