1 files changed, 14 insertions, 8 deletions

diff --git a/fs/xfs/support/ktrace.c b/fs/xfs/support/ktrace.c
index 4e0444c0aca6..0b75d302508f 100644
--- a/fs/xfs/support/ktrace.c
+++ b/fs/xfs/support/ktrace.c
@@ -24,7 +24,7 @@ static int          ktrace_zentries;
 void __init
 ktrace_init(int zentries)
 {
-        ktrace_zentries = zentries;
+        ktrace_zentries = roundup_pow_of_two(zentries);
 
         ktrace_hdr_zone = kmem_zone_init(sizeof(ktrace_t),
                                         "ktrace_hdr");
@@ -47,13 +47,16 @@ ktrace_uninit(void)
  * ktrace_alloc()
  *
  * Allocate a ktrace header and enough buffering for the given
- * number of entries.
+ * number of entries. Round the number of entries up to a
+ * power of 2 so we can do fast masking to get the index from
+ * the atomic index counter.
  */
 ktrace_t *
 ktrace_alloc(int nentries, unsigned int __nocast sleep)
 {
         ktrace_t        *ktp;
         ktrace_entry_t  *ktep;
+        int             entries;
 
         ktp = (ktrace_t*)kmem_zone_alloc(ktrace_hdr_zone, sleep);
 
@@ -70,11 +73,12 @@ ktrace_alloc(int nentries, unsigned int __nocast sleep)
         /*
          * Special treatment for buffers with the ktrace_zentries entries
          */
-        if (nentries == ktrace_zentries) {
+        entries = roundup_pow_of_two(nentries);
+        if (entries == ktrace_zentries) {
                 ktep = (ktrace_entry_t*)kmem_zone_zalloc(ktrace_ent_zone,
                                                             sleep);
         } else {
-                ktep = (ktrace_entry_t*)kmem_zalloc((nentries * sizeof(*ktep)),
+                ktep = (ktrace_entry_t*)kmem_zalloc((entries * sizeof(*ktep)),
                                                             sleep | KM_LARGE);
         }
 
@@ -91,7 +95,9 @@ ktrace_alloc(int nentries, unsigned int __nocast sleep)
         }
 
         ktp->kt_entries  = ktep;
-        ktp->kt_nentries = nentries;
+        ktp->kt_nentries = entries;
+        ASSERT(is_power_of_2(entries));
+        ktp->kt_index_mask = entries - 1;
         atomic_set(&ktp->kt_index, 0);
         ktp->kt_rollover = 0;
         return ktp;
@@ -160,7 +166,7 @@ ktrace_enter(
          * Grab an entry by pushing the index up to the next one.
          */
         index = atomic_add_return(1, &ktp->kt_index);
-        index = (index - 1) % ktp->kt_nentries;
+        index = (index - 1) & ktp->kt_index_mask;
         if (!ktp->kt_rollover && index == ktp->kt_nentries - 1)
                 ktp->kt_rollover = 1;
 
@@ -197,7 +203,7 @@ ktrace_nentries(
         if (ktp == NULL)
                 return 0;
 
-        index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;
+        index = atomic_read(&ktp->kt_index) & ktp->kt_index_mask;
         return (ktp->kt_rollover ? ktp->kt_nentries : index);
 }
 
@@ -223,7 +229,7 @@ ktrace_first(ktrace_t   *ktp, ktrace_snap_t     *ktsp)
         int             nentries;
 
         if (ktp->kt_rollover)
-                index = atomic_read(&ktp->kt_index) % ktp->kt_nentries;
+                index = atomic_read(&ktp->kt_index) & ktp->kt_index_mask;
         else
                 index = 0;