4045 zfs write throttle & i/o scheduler performance work
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Adam Leventhal <ahl@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>

*** 163,172 ****
--- 163,174 ----
  /*
   * Threads
   */
  #define curthread       ((void *)(uintptr_t)thr_self())
  
+ #define kpreempt(x)     yield()
+ 
  typedef struct kthread kthread_t;
  
  #define thread_create(stk, stksize, func, arg, len, pp, state, pri)     \
          zk_thread_create(func, arg)
  #define thread_exit() thr_exit(NULL)