[PATCH] sched: improve efficiency of sched_fork()

Problem:
  sched_fork() has always called scheduler_tick() in some (unlikely)
  circumstances in order to update the current task in light of those
  circumstances.  It has always been the case that the work done by
  scheduler_tick() was more than was required to handle the problem in
  hand but no harm was done except for the waste of a few CPU cycles.

  However, the splitting of scheduler_tick() into two procedures in
  2.6.20-rc1 enables the wasted cycles to be saved as the new procedure
  task_running_tick() does all the work that is required to rectify the
  problem being handled.

Solution:
  Replace the call to scheduler_tick() in sched_fork() with a call to
  task_running_tick().

Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index 5cd833b..b81ed87 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1567,6 +1567,7 @@ int fastcall wake_up_state(struct task_struct *p, unsigned int state)
        return try_to_wake_up(p, state, 0);
 }
 
+static void task_running_tick(struct rq *rq, struct task_struct *p);
 /*
  * Perform scheduler related setup for a newly forked process p.
  * p is forked by current.
@@ -1627,7 +1628,7 @@ void fastcall sched_fork(struct task_struct *p, int clone_flags)
                 * runqueue lock is not a problem.
                 */
                current->time_slice = 1;
-               scheduler_tick();
+               task_running_tick(cpu_rq(cpu), current);
        }
        local_irq_enable();
        put_cpu();