[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20151105135952.GE11639@twins.programming.kicks-ass.net>
Date: Thu, 5 Nov 2015 14:59:52 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>,
LKML <linux-kernel@...r.kernel.org>,
Arjan van de Ven <arjan@...ux.intel.com>,
Paul Turner <pjt@...gle.com>, Len Brown <len.brown@...el.com>,
Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
Tim Chen <tim.c.chen@...ux.intel.com>,
Andi Kleen <andi.kleen@...el.com>,
Rafael Wysocki <rafael.j.wysocki@...el.com>
Subject: Re: [RFC PATCH 3/3] sched: introduce synchronized idle injection
On Tue, Nov 03, 2015 at 02:31:20PM +0100, Peter Zijlstra wrote:
> > @@ -5136,6 +5148,16 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev)
> > struct task_struct *p;
> > int new_tasks;
> >
> > +#ifdef CONFIG_CFS_IDLE_INJECT
> > + if (cfs_rq->force_throttled &&
> > + !idle_cpu(cpu_of(rq)) &&
> > + !unlikely(local_softirq_pending())) {
> > + /* forced idle, pick no task */
> > + trace_sched_cfs_idle_inject(cpu_of(rq), 1);
> > + update_curr(cfs_rq);
> > + return NULL;
> > + }
> > +#endif
> > again:
> > #ifdef CONFIG_FAIR_GROUP_SCHED
> > if (!cfs_rq->nr_running)
>
> So this is horrible...
So this isn't ideal either (I rather liked the previous approach of a
random task assuming idle, but tglx hated that). This should at least
not touch extra cachelines in the hot paths, although it does add a few
extra instructions :/
Very limited testing didn't show anything horrible.
Your throttle would:
raw_spin_lock_irqsave(&rq->lock, flags);
rq->cfs.forced_idle = true;
resched = rq->cfs.runnable;
rq->cfs.runnable = false;
raw_spin_unlock_irqrestore(&rq->lock, flags);
if (resched)
resched_cpu(cpu_of(rq));
And your unthrottle:
raw_spin_lock_irqsave(&rq->lock, flags);
rq->cfs.forced_idle = false;
resched = rq->cfs.runnable = !!rq->cfs.nr_running;
raw_spin_unlock_irqrestore(&rq->lock, flags);
if (resched)
resched_cpu(cpu_of(rq));
---
kernel/sched/fair.c | 13 +++++++++----
kernel/sched/sched.h | 1 +
2 files changed, 10 insertions(+), 4 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 824aa9f..1f0c809 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2341,7 +2341,8 @@ account_entity_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se)
list_add(&se->group_node, &rq->cfs_tasks);
}
#endif
- cfs_rq->nr_running++;
+ if (!cfs_rq->nr_running++ && !cfs_rq->forced_idle)
+ cfs_rq->runnable = true;
}
static void
@@ -2354,7 +2355,8 @@ account_entity_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se)
account_numa_dequeue(rq_of(cfs_rq), task_of(se));
list_del_init(&se->group_node);
}
- cfs_rq->nr_running--;
+ if (!--cfs_rq->nr_running && !cfs_rq->forced_idle)
+ cfs_rq->runnable = false;
}
#ifdef CONFIG_FAIR_GROUP_SCHED
@@ -5204,7 +5206,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev)
again:
#ifdef CONFIG_FAIR_GROUP_SCHED
- if (!cfs_rq->nr_running)
+ if (!cfs_rq->runnable)
goto idle;
if (prev->sched_class != &fair_sched_class)
@@ -5283,7 +5285,7 @@ simple:
cfs_rq = &rq->cfs;
#endif
- if (!cfs_rq->nr_running)
+ if (!cfs_rq->runnable)
goto idle;
put_prev_task(rq, prev);
@@ -5302,6 +5304,9 @@ simple:
return p;
idle:
+ if (cfs_rq->forced_idle)
+ return NULL;
+
/*
* This is OK, because current is on_cpu, which avoids it being picked
* for load-balance and preemption/IRQs are still disabled avoiding
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index efd3bfc..33d355d 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -347,6 +347,7 @@ struct cfs_bandwidth { };
struct cfs_rq {
struct load_weight load;
unsigned int nr_running, h_nr_running;
+ unsigned int runnable, forced_idle;
u64 exec_clock;
u64 min_vruntime;
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists