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mutex: preemption fixes

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The problem is that dropping the spinlock right before schedule is a voluntary
preemption point and can cause a schedule, right after which we schedule again.

Fix this inefficiency by keeping preemption disabled until we schedule, do this
by explicity disabling preemption and providing a schedule() variant that
assumes preemption is already disabled.

Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Peter Zijlstra 2009-01-14 15:36:26 +01:00 • committed by Ingo Molnar
commit 41719b0309
3 changed files with 12 additions and 4 deletions
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10
kernel/sched.c
View file

@ -4538,15 +4538,13 @@ pick_next_task(struct rq *rq, struct task_struct *prev)
/*
* schedule() is the main scheduler function.
*/
asmlinkage void __sched schedule(void)
asmlinkage void __sched __schedule(void)
{
struct task_struct *prev, *next;
unsigned long *switch_count;
struct rq *rq;
int cpu;
need_resched:
preempt_disable();
cpu = smp_processor_id();
rq = cpu_rq(cpu);
rcu_qsctr_inc(cpu);
@ -4603,7 +4601,13 @@ need_resched_nonpreemptible:
if (unlikely(reacquire_kernel_lock(current) < 0))
goto need_resched_nonpreemptible;
}
asmlinkage void __sched schedule(void)
{
need_resched:
preempt_disable();
__schedule();
preempt_enable_no_resched();
if (unlikely(test_thread_flag(TIF_NEED_RESCHED)))
goto need_resched;