distibutions: Extend flexibility of non-uniform random distributions

This change affects options random_distribution and file_service_type.
For pareto, zipf and gauss distribution a contept of `center` is implemented.
It allows to fix in place a value that is most probable to access.
Example:
fio --randseed=1 --ioengine=libaio --rw=randwrite --nrfiles=16 --bs=4k \
    --size=256m --allow_file_create=1 --write_iolog=log.txt \
    --file_service_type=gauss:10:0.1 --filename_format=object.\$filenum --name=x

cat log.txt |grep write |cut -f 1 -d " " |sort |uniq -c | sort -n | \
sed "s/[.]/ /" | while read a b c; do echo $c $b $a; done |sort -n
0 object 13429
1 object 17928
2 object 14724
3 object 7845
4 object 2476
5 object 468
6 object 44
7 object 3
12 object 24
13 object 318
14 object 1795
15 object 6482

Signed-off-by: Adam Kupczyk <akupczyk@redhat.com>

4 files changed, 19 insertions, 10 deletions

diff --git a/lib/gauss.c b/lib/gauss.c
index 3f84dbc6..c64f61e7 100644
--- a/lib/gauss.c
+++ b/lib/gauss.c
@@ -40,11 +40,11 @@ unsigned long long gauss_next(struct gauss_state *gs)
 	if (!gs->disable_hash)
 		sum = __hash_u64(sum);
 
-	return sum % gs->nranges;
+	return (sum + gs->rand_off) % gs->nranges;
 }
 
 void gauss_init(struct gauss_state *gs, unsigned long nranges, double dev,
-		unsigned int seed)
+		double center, unsigned int seed)
 {
 	memset(gs, 0, sizeof(*gs));
 	init_rand_seed(&gs->r, seed, 0);
@@ -55,6 +55,10 @@ void gauss_init(struct gauss_state *gs, unsigned long nranges, double dev,
 		if (gs->stddev > nranges / 2)
 			gs->stddev = nranges / 2;
 	}
+	if (center == -1)
+	  gs->rand_off = 0;
+	else
+	  gs->rand_off = nranges * (center - 0.5);
 }
 
 void gauss_disable_hash(struct gauss_state *gs)
diff --git a/lib/gauss.h b/lib/gauss.h
index 478aa146..19e3a666 100644
--- a/lib/gauss.h
+++ b/lib/gauss.h
@@ -8,11 +8,12 @@ struct gauss_state {
 	struct frand_state r;
 	uint64_t nranges;
 	unsigned int stddev;
+	unsigned int rand_off;
 	bool disable_hash;
 };
 
 void gauss_init(struct gauss_state *gs, unsigned long nranges, double dev,
-		unsigned int seed);
+		double center, unsigned int seed);
 unsigned long long gauss_next(struct gauss_state *gs);
 void gauss_disable_hash(struct gauss_state *gs);
 
diff --git a/lib/zipf.c b/lib/zipf.c
index 321a4fb9..14d7928f 100644
--- a/lib/zipf.c
+++ b/lib/zipf.c
@@ -23,19 +23,21 @@ static void zipf_update(struct zipf_state *zs)
 }
 
 static void shared_rand_init(struct zipf_state *zs, uint64_t nranges,
-			     unsigned int seed)
+			     double center, unsigned int seed)
 {
 	memset(zs, 0, sizeof(*zs));
 	zs->nranges = nranges;
 
 	init_rand_seed(&zs->rand, seed, 0);
 	zs->rand_off = __rand(&zs->rand);
+	if (center != -1)
+		zs->rand_off = nranges * center;
 }
 
 void zipf_init(struct zipf_state *zs, uint64_t nranges, double theta,
-	       unsigned int seed)
+	       double center, unsigned int seed)
 {
-	shared_rand_init(zs, nranges, seed);
+	shared_rand_init(zs, nranges, center, seed);
 
 	zs->theta = theta;
 	zs->zeta2 = pow(1.0, zs->theta) + pow(0.5, zs->theta);
@@ -71,9 +73,9 @@ uint64_t zipf_next(struct zipf_state *zs)
 }
 
 void pareto_init(struct zipf_state *zs, uint64_t nranges, double h,
-		 unsigned int seed)
+		 double center, unsigned int seed)
 {
-	shared_rand_init(zs, nranges, seed);
+	shared_rand_init(zs, nranges, center, seed);
 	zs->pareto_pow = log(h) / log(1.0 - h);
 }
 
diff --git a/lib/zipf.h b/lib/zipf.h
index 16b65f57..332e3b2f 100644
--- a/lib/zipf.h
+++ b/lib/zipf.h
@@ -16,10 +16,12 @@ struct zipf_state {
 	bool disable_hash;
 };
 
-void zipf_init(struct zipf_state *zs, uint64_t nranges, double theta, unsigned int seed);
+void zipf_init(struct zipf_state *zs, uint64_t nranges, double theta,
+	       double center, unsigned int seed);
 uint64_t zipf_next(struct zipf_state *zs);
 
-void pareto_init(struct zipf_state *zs, uint64_t nranges, double h, unsigned int seed);
+void pareto_init(struct zipf_state *zs, uint64_t nranges, double h,
+		 double center, unsigned int seed);
 uint64_t pareto_next(struct zipf_state *zs);
 void zipf_disable_hash(struct zipf_state *zs);