lib/rand: improve __fill_random_buf()

axboe · axboe · commit aa75fc9db6b9 · 2022-07-01T15:02:06.000-06:00
This won't be equivalent to what we have, but I _think_ the randomness
is good enough for this purpose.

This improves performance by about 30% for me, tested on both aarch64
and x86-64.

Signed-off-by: Jens Axboe &lt;axboe@kernel.dk&gt;
diff --git a/lib/rand.c b/lib/rand.c
@@ -103,8 +103,7 @@ void __fill_random_buf(void *buf, unsigned int len, uint64_t seed)
 
 	for (; b != e; ++b) {
 		*b = seed;
-		seed *= GOLDEN_RATIO_PRIME;
-		seed >>= 3;
+		seed *= GOLDEN_RATIO_64;
 	}
 
 	if (fio_unlikely(rest))

Original file line number	Diff line number	Diff line change
`@@ -103,8 +103,7 @@ void __fill_random_buf(void *buf, unsigned int len, uint64_t seed)`
`103`	`103`
`104`	`104`	`for (; b != e; ++b) {`
`105`	`105`	`*b = seed;`
`106`		`- seed *= GOLDEN_RATIO_PRIME;`
`107`		`- seed >>= 3;`
	`106`	`+ seed *= GOLDEN_RATIO_64;`
`108`	`107`	`}`
`109`	`108`
`110`	`109`	`if (fio_unlikely(rest))`