- * We can use the eieio instruction for wmb, but since it doesn't
- * give any ordering guarantees about loads, we have to use the
- * stronger but slower sync instruction for mb and rmb.
+ * We have to use the sync instructions for mb(), since lwsync doesn't
+ * order loads with respect to previous stores. Lwsync is fine for
+ * rmb(), though.
+ * For wmb(), we use sync since wmb is used in drivers to order
+ * stores to system memory with respect to writes to the device.
+ * However, smp_wmb() can be a lighter-weight eieio barrier on
+ * SMP since it is only used to order updates to system memory.