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authorOleg Nesterov <oleg@redhat.com>2010-05-19 14:57:11 +0200
committerIngo Molnar <mingo@elte.hu>2010-06-09 10:34:50 +0200
commit246d86b51845063e4b06b27579990492dc5fa317 (patch)
tree3f60fc00b8cc587826cc76e31a1afb92353d08dd /kernel/sched.c
parentc676329abb2b8359d9a5d734dec0c81779823fd6 (diff)
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sched: Simplify the reacquire_kernel_lock() logic
- Contrary to what 6d558c3a says, there is no need to reload prev = rq->curr after the context switch. You always schedule back to where you came from, prev must be equal to current even if cpu/rq was changed. - This also means reacquire_kernel_lock() can use prev instead of current. - No need to reassign switch_count if reacquire_kernel_lock() reports need_resched(), we can just move the initial assignment down, under the "need_resched_nonpreemptible:" label. - Try to update the comment after context_switch(). Signed-off-by: Oleg Nesterov <oleg@redhat.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <20100519125711.GA30199@redhat.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/sched.c')
-rw-r--r--kernel/sched.c13
1 files changed, 6 insertions, 7 deletions
diff --git a/kernel/sched.c b/kernel/sched.c
index 3abd8f780da..f37a9618fac 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3636,7 +3636,6 @@ need_resched:
rq = cpu_rq(cpu);
rcu_note_context_switch(cpu);
prev = rq->curr;
- switch_count = &prev->nivcsw;
release_kernel_lock(prev);
need_resched_nonpreemptible:
@@ -3649,6 +3648,7 @@ need_resched_nonpreemptible:
raw_spin_lock_irq(&rq->lock);
clear_tsk_need_resched(prev);
+ switch_count = &prev->nivcsw;
if (prev->state && !(preempt_count() & PREEMPT_ACTIVE)) {
if (unlikely(signal_pending_state(prev->state, prev))) {
prev->state = TASK_RUNNING;
@@ -3689,8 +3689,10 @@ need_resched_nonpreemptible:
context_switch(rq, prev, next); /* unlocks the rq */
/*
- * the context switch might have flipped the stack from under
- * us, hence refresh the local variables.
+ * The context switch have flipped the stack from under us
+ * and restored the local variables which were saved when
+ * this task called schedule() in the past. prev == current
+ * is still correct, but it can be moved to another cpu/rq.
*/
cpu = smp_processor_id();
rq = cpu_rq(cpu);
@@ -3699,11 +3701,8 @@ need_resched_nonpreemptible:
post_schedule(rq);
- if (unlikely(reacquire_kernel_lock(current) < 0)) {
- prev = rq->curr;
- switch_count = &prev->nivcsw;
+ if (unlikely(reacquire_kernel_lock(prev)))
goto need_resched_nonpreemptible;
- }
preempt_enable_no_resched();
if (need_resched())