[PATCH] sched: consolidate sbe sbf

Consolidate balance-on-exec with balance-on-fork.  This is made easy by the
sched-domains RCU patches.

As well as the general goodness of code reduction, this allows the runqueues
to be unlocked during balance-on-fork.

schedstats is a problem.  Maybe just have balance-on-event instead of
distinguishing fork and exec?

Signed-off-by: Nick Piggin <nickpiggin@yahoo.com.au>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 12 insertions, 9 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index a28d11e10877..2c7806873bfd 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1003,9 +1003,6 @@ static task_t *copy_process(unsigned long clone_flags,
         p->pdeath_signal = 0;
         p->exit_state = 0;
 
-        /* Perform scheduler related setup */
-        sched_fork(p);
-
         /*
          * Ok, make it visible to the rest of the system.
          * We dont wake it up yet.
@@ -1014,18 +1011,24 @@ static task_t *copy_process(unsigned long clone_flags,
         INIT_LIST_HEAD(&p->ptrace_children);
         INIT_LIST_HEAD(&p->ptrace_list);
 
+        /* Perform scheduler related setup. Assign this task to a CPU. */
+        sched_fork(p, clone_flags);
+
         /* Need tasklist lock for parent etc handling! */
         write_lock_irq(&tasklist_lock);
 
         /*
-         * The task hasn't been attached yet, so cpus_allowed mask cannot
-         * have changed. The cpus_allowed mask of the parent may have
-         * changed after it was copied first time, and it may then move to
-         * another CPU - so we re-copy it here and set the child's CPU to
-         * the parent's CPU. This avoids alot of nasty races.
+         * The task hasn't been attached yet, so its cpus_allowed mask will
+         * not be changed, nor will its assigned CPU.
+         *
+         * The cpus_allowed mask of the parent may have changed after it was
+         * copied first time - so re-copy it here, then check the child's CPU
+         * to ensure it is on a valid CPU (and if not, just force it back to
+         * parent's CPU). This avoids alot of nasty races.
          */
         p->cpus_allowed = current->cpus_allowed;
-        set_task_cpu(p, smp_processor_id());
+        if (unlikely(!cpu_isset(task_cpu(p), p->cpus_allowed)))
+                set_task_cpu(p, smp_processor_id());
 
         /*
          * Check for pending SIGKILL! The new thread should not be allowed