Hi all,
please review the attached patch to remove the two remaining MI uses of
random(9). Neither should be in a performance critical code path and
both may actually benefit from the better distribution. The vfs_bio.c
change is a bit more involved as I am trying to replace a 32bit division
with a long multiplication, which should be cheaper pretty much
anywhere.
Joerg
Index: ufs/ffs/ffs_alloc.c
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/ufs/ffs/ffs_alloc.c,v
retrieving revision 1.146
diff -u -p -r1.146 ffs_alloc.c
--- ufs/ffs/ffs_alloc.c 25 Jul 2014 08:24:31 -0000 1.146
+++ ufs/ffs/ffs_alloc.c 8 Sep 2014 13:03:50 -0000
@@ -90,6 +90,7 @@ __KERNEL_RCSID(0, "$NetBSD: ffs_alloc.c,
#include <sys/syslog.h>
#include <sys/vnode.h>
#include <sys/wapbl.h>
+#include <sys/cprng.h>
#include <miscfs/specfs/specdev.h>
#include <ufs/ufs/quota.h>
@@ -697,7 +698,7 @@ ffs_dirpref(struct inode *pip)
* Force allocation in another cg if creating a first level dir.
*/
if (ITOV(pip)->v_vflag & VV_ROOT) {
- prefcg = random() % fs->fs_ncg;
+ prefcg = cprng_fast32() % fs->fs_ncg;
mincg = prefcg;
minndir = fs->fs_ipg;
for (cg = prefcg; cg < fs->fs_ncg; cg++)
Index: kern/vfs_bio.c
===================================================================
RCS file: /home/joerg/repo/netbsd/src/sys/kern/vfs_bio.c,v
retrieving revision 1.251
diff -u -p -r1.251 vfs_bio.c
--- kern/vfs_bio.c 5 Sep 2014 05:57:21 -0000 1.251
+++ kern/vfs_bio.c 8 Sep 2014 18:00:47 -0000
@@ -143,6 +143,7 @@ __KERNEL_RCSID(0, "$NetBSD: vfs_bio.c,v
#include <sys/cpu.h>
#include <sys/wapbl.h>
#include <sys/bitops.h>
+#include <sys/cprng.h>
#include <uvm/uvm.h> /* extern struct uvm uvm */
@@ -532,7 +533,7 @@ bufinit2(void)
static int
buf_lotsfree(void)
{
- int guess, thresh;
+ u_long guess;
/* Always allocate if less than the low water mark. */
if (bufmem < bufmem_lowater)
@@ -548,16 +549,13 @@ buf_lotsfree(void)
/*
* The probabily of getting a new allocation is inversely
- * proportional to the current size of the cache, using
- * a granularity of 16 steps.
+ * proportional to the current size of the cache above the low
+ * water mark. Divide into 16 steps to avoid overflows.
*/
- guess = random() & 0x0000000fL;
+ guess = cprng_fast32() % 16;
- /* Don't use "16 * bufmem" here to avoid a 32-bit overflow. */
- thresh = (bufmem - bufmem_lowater) /
- ((bufmem_hiwater - bufmem_lowater) / 16);
-
- if (guess >= thresh)
+ if ((bufmem_hiwater - bufmem_lowater) / 16 * guess >=
+ (bufmem - bufmem_lowater))
return 1;
/* Otherwise don't allocate. */
