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Message-ID: <20250220093257.9380-10-kprateek.nayak@amd.com>
Date: Thu, 20 Feb 2025 09:32:44 +0000
From: K Prateek Nayak <kprateek.nayak@....com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>,
Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
<vincent.guittot@...aro.org>, Valentin Schneider <vschneid@...hat.com>, "Ben
Segall" <bsegall@...gle.com>, Thomas Gleixner <tglx@...utronix.de>, "Andy
Lutomirski" <luto@...nel.org>, <linux-kernel@...r.kernel.org>
CC: Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt
<rostedt@...dmis.org>, Mel Gorman <mgorman@...e.de>, "Sebastian Andrzej
Siewior" <bigeasy@...utronix.de>, Clark Williams <clrkwllms@...nel.org>,
<linux-rt-devel@...ts.linux.dev>, Tejun Heo <tj@...nel.org>, "Frederic
Weisbecker" <frederic@...nel.org>, Barret Rhoden <brho@...gle.com>, "Petr
Mladek" <pmladek@...e.com>, Josh Don <joshdon@...gle.com>, Qais Yousef
<qyousef@...alina.io>, "Paul E. McKenney" <paulmck@...nel.org>, David Vernet
<dvernet@...a.com>, K Prateek Nayak <kprateek.nayak@....com>, "Gautham R.
Shenoy" <gautham.shenoy@....com>, Swapnil Sapkal <swapnil.sapkal@....com>
Subject: [RFC PATCH 09/22] sched/fair: Introduce cfs_rq throttled states in preparation for partial throttling
On introduction of throttle deferral, cfs_rq on encountering a throttle
event with kernel mode preempted entities will be marked partially
throttled allowing only these kernel mode entities to run until they
sleep or exit to userspace.
Introduce "throttled_state" enum to define the three throttle states -
CFS_UNTHROTTLED, CFS_THROTTLED_PARTIAL, and CFS_THROTTLED. In addition
to cfs_rq_throttled() which will now track both partial and complete
throttle, introduce a new helper cfs_rq_h_throttled() to detect a
completely throttled hierarchy.
Convert appropriate cfs_rq_throttled() checks to cfs_rq_h_throttled() to
guard logic that only concerns with a complete throttle. Also take the
opportunity to convert any open coded references to cfs_tr->throttled to
use one of the two helpers.
Signed-off-by: K Prateek Nayak <kprateek.nayak@....com>
---
kernel/sched/fair.c | 67 ++++++++++++++++++++++++++++++++++-----------
1 file changed, 51 insertions(+), 16 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4fd70012b479..c84cd2d92343 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5340,7 +5340,11 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
}
static void check_enqueue_throttle(struct cfs_rq *cfs_rq);
+
+/* cfs_rq is throttled either completely or partially */
static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq);
+/* cfs_rq is throttled completely and the hierarchy is frozen */
+static inline int cfs_rq_h_throttled(struct cfs_rq *cfs_rq);
static void
requeue_delayed_entity(struct sched_entity *se);
@@ -5404,7 +5408,7 @@ enqueue_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
#ifdef CONFIG_CFS_BANDWIDTH
struct rq *rq = rq_of(cfs_rq);
- if (cfs_rq_throttled(cfs_rq) && !cfs_rq->throttled_clock)
+ if (cfs_rq_h_throttled(cfs_rq) && !cfs_rq->throttled_clock)
cfs_rq->throttled_clock = rq_clock(rq);
if (!cfs_rq->throttled_clock_self)
cfs_rq->throttled_clock_self = rq_clock(rq);
@@ -5448,7 +5452,7 @@ static void set_delayed(struct sched_entity *se)
struct cfs_rq *cfs_rq = cfs_rq_of(se);
cfs_rq->h_nr_runnable--;
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
break;
}
}
@@ -5470,7 +5474,7 @@ static void clear_delayed(struct sched_entity *se)
struct cfs_rq *cfs_rq = cfs_rq_of(se);
cfs_rq->h_nr_runnable++;
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
break;
}
}
@@ -5817,7 +5821,7 @@ static void __account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
if (likely(cfs_rq->runtime_remaining > 0))
return;
- if (cfs_rq->throttled)
+ if (cfs_rq_throttled(cfs_rq))
return;
/*
* if we're unable to extend our runtime we resched so that the active
@@ -5836,11 +5840,37 @@ void account_cfs_rq_runtime(struct cfs_rq *cfs_rq, u64 delta_exec)
__account_cfs_rq_runtime(cfs_rq, delta_exec);
}
+/* cfs_rq->throttled states */
+enum throttle_state {
+ /*
+ * cfs_rq is unthrottled; All the queued entities
+ * can be picked to run.
+ */
+ CFS_UNTHROTTLED = 0,
+ /*
+ * cfs_rq is only marked throttled. There are kernel
+ * mode preempted entities that are still runnable.
+ * PELT is not frozen yet.
+ */
+ CFS_THROTTLED_PARTIAL,
+ /*
+ * cfs_rq is fully throttled with PELT frozen. There
+ * are no entities that are considered runnable under
+ * throttle.
+ */
+ CFS_THROTTLED
+};
+
static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
{
return cfs_bandwidth_used() && cfs_rq->throttled;
}
+static inline int cfs_rq_h_throttled(struct cfs_rq *cfs_rq)
+{
+ return cfs_bandwidth_used() && (cfs_rq->throttled == CFS_THROTTLED);
+}
+
/* check whether cfs_rq, or any parent, is throttled */
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
@@ -6011,7 +6041,7 @@ static bool throttle_cfs_rq(struct cfs_rq *cfs_rq)
* Note: distribution will already see us throttled via the
* throttled-list. rq->lock protects completion.
*/
- cfs_rq->throttled = 1;
+ cfs_rq->throttled = CFS_THROTTLED;
SCHED_WARN_ON(cfs_rq->throttled_clock);
if (cfs_rq->nr_queued)
cfs_rq->throttled_clock = rq_clock(rq);
@@ -6028,7 +6058,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
se = cfs_rq->tg->se[cpu_of(rq)];
- cfs_rq->throttled = 0;
+ cfs_rq->throttled = CFS_UNTHROTTLED;
update_rq_clock(rq);
@@ -6080,7 +6110,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
qcfs_rq->h_nr_idle += idle_delta;
/* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(qcfs_rq))
+ if (cfs_rq_h_throttled(qcfs_rq))
goto unthrottle_throttle;
}
@@ -6098,7 +6128,7 @@ void unthrottle_cfs_rq(struct cfs_rq *cfs_rq)
qcfs_rq->h_nr_idle += idle_delta;
/* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(qcfs_rq))
+ if (cfs_rq_h_throttled(qcfs_rq))
goto unthrottle_throttle;
}
@@ -6503,7 +6533,7 @@ static bool check_cfs_rq_runtime(struct cfs_rq *cfs_rq)
* it's possible for a throttled entity to be forced into a running
* state (e.g. set_curr_task), in this case we're finished.
*/
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
return true;
return throttle_cfs_rq(cfs_rq);
@@ -7029,6 +7059,11 @@ static inline int cfs_rq_throttled(struct cfs_rq *cfs_rq)
return 0;
}
+static inline int cfs_rq_h_throttled(struct cfs_rq *cfs_rq)
+{
+ return 0;
+}
+
static inline int throttled_hierarchy(struct cfs_rq *cfs_rq)
{
return 0;
@@ -7310,7 +7345,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
h_nr_idle = 1;
/* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
goto enqueue_throttle;
flags = ENQUEUE_WAKEUP;
@@ -7337,7 +7372,7 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
h_nr_idle = 1;
/* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
goto enqueue_throttle;
}
@@ -7431,7 +7466,7 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
h_nr_idle = h_nr_queued;
/* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
return 0;
/* Don't dequeue parent if it has other entities besides us */
@@ -7472,8 +7507,8 @@ static int dequeue_entities(struct rq *rq, struct sched_entity *se, int flags)
if (cfs_rq_is_idle(cfs_rq))
h_nr_idle = h_nr_queued;
- /* end evaluation on encountering a throttled cfs_rq */
- if (cfs_rq_throttled(cfs_rq))
+ /* end evaluation on encountering a throttled cfs_rq hierarchy */
+ if (cfs_rq_h_throttled(cfs_rq))
return 0;
}
@@ -13519,7 +13554,7 @@ static void propagate_entity_cfs_rq(struct sched_entity *se)
{
struct cfs_rq *cfs_rq = cfs_rq_of(se);
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
return;
if (!throttled_hierarchy(cfs_rq))
@@ -13533,7 +13568,7 @@ static void propagate_entity_cfs_rq(struct sched_entity *se)
update_load_avg(cfs_rq, se, UPDATE_TG);
- if (cfs_rq_throttled(cfs_rq))
+ if (cfs_rq_h_throttled(cfs_rq))
break;
if (!throttled_hierarchy(cfs_rq))
--
2.43.0
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