Optimize small random numbers generation

In all places except two spa_get_random() is used for small values,
and the consumers do not require well seeded high quality values.
Switch those two exceptions directly to random_get_pseudo_bytes()
and optimize spa_get_random(), renaming it to random_in_range(),
since it is not related to SPA or ZFS in general.

On FreeBSD directly map random_in_range() to new prng32_bounded() KPI
added in FreeBSD 13.  On Linux and in user-space just reduce the type
used to uint32_t to avoid more expensive 64bit division.

Reviewed-by: Ryan Moeller <[email protected]>
Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Alexander Motin <[email protected]>
Sponsored-By: iXsystems, Inc.
Closes #12183

4 files changed, 52 insertions, 1 deletions

diff --git a/include/os/freebsd/spl/sys/random.h b/include/os/freebsd/spl/sys/random.h
index b3c9115f5..746275e53 100644
--- a/include/os/freebsd/spl/sys/random.h
+++ b/include/os/freebsd/spl/sys/random.h
@@ -30,6 +30,9 @@
 #define	_OPENSOLARIS_SYS_RANDOM_H_
 
 #include_next <sys/random.h>
+#if  __FreeBSD_version >= 1300108
+#include <sys/prng.h>
+#endif
 
 static inline int
 random_get_bytes(uint8_t *p, size_t s)
@@ -45,4 +48,23 @@ random_get_pseudo_bytes(uint8_t *p, size_t s)
 	return (0);
 }
 
+static inline uint32_t
+random_in_range(uint32_t range)
+{
+#if  __FreeBSD_version >= 1300108
+	return (prng32_bounded(range));
+#else
+	uint32_t r;
+
+	ASSERT(range != 0);
+
+	if (range == 1)
+		return (0);
+
+	(void) random_get_pseudo_bytes((void *)&r, sizeof (r));
+
+	return (r % range);
+#endif
+}
+
 #endif	/* !_OPENSOLARIS_SYS_RANDOM_H_ */
diff --git a/include/os/linux/spl/sys/random.h b/include/os/linux/spl/sys/random.h
index 1b8cb60d0..2c446e155 100644
--- a/include/os/linux/spl/sys/random.h
+++ b/include/os/linux/spl/sys/random.h
@@ -36,4 +36,19 @@ random_get_bytes(uint8_t *ptr, size_t len)
 
 extern int random_get_pseudo_bytes(uint8_t *ptr, size_t len);
 
+static __inline__ uint32_t
+random_in_range(uint32_t range)
+{
+	uint32_t r;
+
+	ASSERT(range != 0);
+
+	if (range == 1)
+		return (0);
+
+	(void) random_get_pseudo_bytes((void *)&r, sizeof (r));
+
+	return (r % range);
+}
+
 #endif	/* _SPL_RANDOM_H */
diff --git a/include/sys/spa.h b/include/sys/spa.h
index 9dd47a1eb..532926e12 100644
--- a/include/sys/spa.h
+++ b/include/sys/spa.h
@@ -1086,7 +1086,6 @@ extern spa_t *spa_by_guid(uint64_t pool_guid, uint64_t device_guid);
 extern boolean_t spa_guid_exists(uint64_t pool_guid, uint64_t device_guid);
 extern char *spa_strdup(const char *);
 extern void spa_strfree(char *);
-extern uint64_t spa_get_random(uint64_t range);
 extern uint64_t spa_generate_guid(spa_t *spa);
 extern void snprintf_blkptr(char *buf, size_t buflen, const blkptr_t *bp);
 extern void spa_freeze(spa_t *spa);
diff --git a/include/sys/zfs_context.h b/include/sys/zfs_context.h
index ffb20e1fe..dbeb323ba 100644
--- a/include/sys/zfs_context.h
+++ b/include/sys/zfs_context.h
@@ -640,6 +640,21 @@ extern int lowbit64(uint64_t i);
 extern int random_get_bytes(uint8_t *ptr, size_t len);
 extern int random_get_pseudo_bytes(uint8_t *ptr, size_t len);
 
+static __inline__ uint32_t
+random_in_range(uint32_t range)
+{
+	uint32_t r;
+
+	ASSERT(range != 0);
+
+	if (range == 1)
+		return (0);
+
+	(void) random_get_pseudo_bytes((void *)&r, sizeof (r));
+
+	return (r % range);
+}
+
 extern void kernel_init(int mode);
 extern void kernel_fini(void);
 extern void random_init(void);