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sched: Fix sched_exec() balancing

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Since we access ->cpus_allowed without holding rq->lock we need
a retry loop to validate the result, this comes for near free
when we merge sched_migrate_task() into sched_exec() since that
already does the needed check.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
LKML-Reference: <20091216170517.884743662@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Peter Zijlstra 2009-12-16 18:04:37 +01:00 committed by Ingo Molnar
parent e2912009fb
commit 3802290628
1 changed files with 23 additions and 22 deletions
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45
kernel/sched.c
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@ -2322,7 +2322,7 @@ void task_oncpu_function_call(struct task_struct *p,
*
* - fork, @p is stable because it isn't on the tasklist yet
*
* - exec, @p is unstable XXX
* - exec, @p is unstable, retry loop
*
* - wake-up, we serialize ->cpus_allowed against TASK_WAKING so
* we should be good.
@ -3132,21 +3132,36 @@ static void double_rq_unlock(struct rq *rq1, struct rq *rq2)
}
/*
* If dest_cpu is allowed for this process, migrate the task to it.
* This is accomplished by forcing the cpu_allowed mask to only
* allow dest_cpu, which will force the cpu onto dest_cpu. Then
* the cpu_allowed mask is restored.
* sched_exec - execve() is a valuable balancing opportunity, because at
* this point the task has the smallest effective memory and cache footprint.
*/
static void sched_migrate_task(struct task_struct *p, int dest_cpu)
void sched_exec(void)
{
struct task_struct *p = current;
struct migration_req req;
int dest_cpu, this_cpu;
unsigned long flags;
struct rq *rq;
again:
this_cpu = get_cpu();
dest_cpu = select_task_rq(p, SD_BALANCE_EXEC, 0);
if (dest_cpu == this_cpu) {
put_cpu();
return;
}
rq = task_rq_lock(p, &flags);
put_cpu();
/*
* select_task_rq() can race against ->cpus_allowed
*/
if (!cpumask_test_cpu(dest_cpu, &p->cpus_allowed)
|| unlikely(!cpu_active(dest_cpu)))
goto out;
|| unlikely(!cpu_active(dest_cpu))) {
task_rq_unlock(rq, &flags);
goto again;
}
/* force the process onto the specified CPU */
if (migrate_task(p, dest_cpu, &req)) {
@ -3161,23 +3176,9 @@ static void sched_migrate_task(struct task_struct *p, int dest_cpu)
return;
}
out:
task_rq_unlock(rq, &flags);
}
/*
* sched_exec - execve() is a valuable balancing opportunity, because at
* this point the task has the smallest effective memory and cache footprint.
*/
void sched_exec(void)
{
int new_cpu, this_cpu = get_cpu();
new_cpu = select_task_rq(current, SD_BALANCE_EXEC, 0);
put_cpu();
if (new_cpu != this_cpu)
sched_migrate_task(current, new_cpu);
}
/*
* pull_task - move a task from a remote runqueue to the local runqueue.
* Both runqueues must be locked.