[PATCH 3/8] Add a PF flag for ksoftirqd identification

Venkatesh Pallipadi
2010-10-05T00:03:59Z

To account softirq time cleanly in scheduler, we need to identify whether
softirq is invoked in ksoftirqd context or softirq at hardirq tail context.
Add PF_KSOFTIRQD for that purpose.

As all PF flag bits are currently taken, create space by moving one of the
infrequently used bits (PF_THREAD_BOUND) down in task_struct to be along
with some other state fields.

Signed-off-by: Venkatesh Pallipadi <venki@google.com>
---
include/linux/sched.h | 3 ++-
kernel/cpuset.c | 2 +-
kernel/kthread.c | 2 +-
kernel/sched.c | 2 +-
kernel/softirq.c | 1 +
kernel/workqueue.c | 6 +++---
6 files changed, 9 insertions(+), 7 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 126457e..43064cd 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1234,6 +1234,7 @@ struct task_struct {

/* Revert to default priority/policy when forking */
unsigned sched_reset_on_fork:1;
+ unsigned sched_thread_bound:1; /* Thread bound to specific cpu */

pid_t pid;
pid_t tgid;
@@ -1708,7 +1709,7 @@ extern void thread_group_times(struct task_struct *p, cputime_t *ut, cputime_t *
#define PF_SWAPWRITE 0x00800000 /* Allowed to write to swap */
#define PF_SPREAD_PAGE 0x01000000 /* Spread page cache over cpuset */
#define PF_SPREAD_SLAB 0x02000000 /* Spread some slab caches over cpuset */
-#define PF_THREAD_BOUND 0x04000000 /* Thread bound to specific cpu */
+#define PF_KSOFTIRQD 0x04000000 /* I am ksoftirqd */
#define PF_MCE_EARLY 0x08000000 /* Early kill for mce process policy */
#define PF_MEMPOLICY 0x10000000 /* Non-default NUMA mempolicy */
#define PF_MUTEX_TESTER 0x20000000 /* Thread belongs to the rt mutex tester */
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index b23c097..8a2eb02 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1394,7 +1394,7 @@ static int cpuset_can_attach(struct cgroup_subsys *ss, struct cgroup *cont,
* set_cpus_allowed_ptr() on all attached tasks before cpus_allowed may
* be changed.
*/
- if (tsk->flags & PF_THREAD_BOUND)
+ if (tsk->sched_thread_bound)
return -EINVAL;

ret = security_task_setscheduler(tsk, 0, NULL);
diff --git a/kernel/kthread.c b/kernel/kthread.c
index 2dc3786..6b51a4c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -185,7 +185,7 @@ void kthread_bind(struct task_struct *p, unsigned int cpu)

p->cpus_allowed = cpumask_of_cpu(cpu);
p->rt.nr_cpus_allowed = 1;
- p->flags |= PF_THREAD_BOUND;
+ p->sched_thread_bound = 1;
}
EXPORT_SYMBOL(kthread_bind);

diff --git a/kernel/sched.c b/kernel/sched.c
index b6e714b..c13fae6 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5464,7 +5464,7 @@ again:
goto out;
}

- if (unlikely((p->flags & PF_THREAD_BOUND) && p != current &&
+ if (unlikely(p->sched_thread_bound && p != current &&
!cpumask_equal(&p->cpus_allowed, new_mask))) {
ret = -EINVAL;
goto out;
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 988dfbe..267f7b7 100644
--- a/kernel/softirq.c
+++ b/kernel/softirq.c
@@ -713,6 +713,7 @@ static int run_ksoftirqd(void * __bind_cpu)
{
set_current_state(TASK_INTERRUPTIBLE);

+ current->flags |= PF_KSOFTIRQD;
while (!kthread_should_stop()) {
preempt_disable();
if (!local_softirq_pending()) {
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index f77afd9..7146ee6 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1340,12 +1340,12 @@ static struct worker *create_worker(struct global_cwq *gcwq, bool bind)
/*
* A rogue worker will become a regular one if CPU comes
* online later on. Make sure every worker has
- * PF_THREAD_BOUND set.
+ * sched_thread_bound set.
*/
if (bind && !on_unbound_cpu)
kthread_bind(worker->task, gcwq->cpu);
else {
- worker->task->flags |= PF_THREAD_BOUND;
+ worker->task->sched_thread_bound = 1;
if (on_unbound_cpu)
worker->flags |= WORKER_UNBOUND;
}
@@ -2817,7 +2817,7 @@ struct workqueue_struct *__alloc_workqueue_key(const char *name,
if (IS_ERR(rescuer->task))
goto err;

- rescuer->task->flags |= PF_THREAD_BOUND;
+ rescuer->task->sched_thread_bound = 1;
wake_up_process(rescuer->task);
}

--
1.7.1