From: Vineeth Remanan Pillai <vpillai@digitalocean.com>
To: Nishanth Aravamudan <naravamudan@digitalocean.com>,
Julien Desfossez <jdesfossez@digitalocean.com>,
Peter Zijlstra <peterz@infradead.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
mingo@kernel.org, tglx@linutronix.de, pjt@google.com,
torvalds@linux-foundation.org
Cc: linux-kernel@vger.kernel.org, subhra.mazumdar@oracle.com,
fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com,
Phil Auld <pauld@redhat.com>, Aaron Lu <aaron.lwe@gmail.com>,
Aubrey Li <aubrey.intel@gmail.com>,
Valentin Schneider <valentin.schneider@arm.com>,
Mel Gorman <mgorman@techsingularity.net>,
Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: [RFC PATCH v2 08/17] sched: Rework pick_next_task() slow-path
Date: Tue, 23 Apr 2019 16:18:13 +0000 [thread overview]
Message-ID: <b78cac7afa840d5e7f3602e5ad13d1ae3a3bf3a0.1556025155.git.vpillai@digitalocean.com> (raw)
In-Reply-To: <cover.1556025155.git.vpillai@digitalocean.com>
In-Reply-To: <cover.1556025155.git.vpillai@digitalocean.com>
From: Peter Zijlstra (Intel) <peterz@infradead.org>
Avoid the RETRY_TASK case in the pick_next_task() slow path.
By doing the put_prev_task() early, we get the rt/deadline pull done,
and by testing rq->nr_running we know if we need newidle_balance().
This then gives a stable state to pick a task from.
Since the fast-path is fair only; it means the other classes will
always have pick_next_task(.prev=NULL, .rf=NULL) and we can simplify.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/sched/core.c | 19 ++++++++++++-------
kernel/sched/deadline.c | 30 ++----------------------------
kernel/sched/fair.c | 9 ++++++---
kernel/sched/idle.c | 4 +++-
kernel/sched/rt.c | 29 +----------------------------
kernel/sched/sched.h | 13 ++++++++-----
kernel/sched/stop_task.c | 3 ++-
7 files changed, 34 insertions(+), 73 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9dfa0c53deb3..b883c70674ba 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3363,7 +3363,7 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
p = fair_sched_class.pick_next_task(rq, prev, rf);
if (unlikely(p == RETRY_TASK))
- goto again;
+ goto restart;
/* Assumes fair_sched_class->next == idle_sched_class */
if (unlikely(!p))
@@ -3372,14 +3372,19 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
return p;
}
-again:
+restart:
+ /*
+ * Ensure that we put DL/RT tasks before the pick loop, such that they
+ * can PULL higher prio tasks when we lower the RQ 'priority'.
+ */
+ prev->sched_class->put_prev_task(rq, prev, rf);
+ if (!rq->nr_running)
+ newidle_balance(rq, rf);
+
for_each_class(class) {
- p = class->pick_next_task(rq, prev, rf);
- if (p) {
- if (unlikely(p == RETRY_TASK))
- goto again;
+ p = class->pick_next_task(rq, NULL, NULL);
+ if (p)
return p;
- }
}
/* The idle class should always have a runnable task: */
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 56791c0318a2..249310e68592 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1730,39 +1730,13 @@ pick_next_task_dl(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *p;
struct dl_rq *dl_rq;
- dl_rq = &rq->dl;
-
- if (need_pull_dl_task(rq, prev)) {
- /*
- * This is OK, because current is on_cpu, which avoids it being
- * picked for load-balance and preemption/IRQs are still
- * disabled avoiding further scheduler activity on it and we're
- * being very careful to re-start the picking loop.
- */
- rq_unpin_lock(rq, rf);
- pull_dl_task(rq);
- rq_repin_lock(rq, rf);
- /*
- * pull_dl_task() can drop (and re-acquire) rq->lock; this
- * means a stop task can slip in, in which case we need to
- * re-start task selection.
- */
- if (rq->stop && task_on_rq_queued(rq->stop))
- return RETRY_TASK;
- }
+ WARN_ON_ONCE(prev || rf);
- /*
- * When prev is DL, we may throttle it in put_prev_task().
- * So, we update time before we check for dl_nr_running.
- */
- if (prev->sched_class == &dl_sched_class)
- update_curr_dl(rq);
+ dl_rq = &rq->dl;
if (unlikely(!dl_rq->dl_nr_running))
return NULL;
- put_prev_task(rq, prev);
-
dl_se = pick_next_dl_entity(rq, dl_rq);
BUG_ON(!dl_se);
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 41ec5e68e1c5..c055bad249a9 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6950,7 +6950,7 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
goto idle;
#ifdef CONFIG_FAIR_GROUP_SCHED
- if (prev->sched_class != &fair_sched_class)
+ if (!prev || prev->sched_class != &fair_sched_class)
goto simple;
/*
@@ -7027,8 +7027,8 @@ pick_next_task_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
goto done;
simple:
#endif
-
- put_prev_task(rq, prev);
+ if (prev)
+ put_prev_task(rq, prev);
do {
se = pick_next_entity(cfs_rq, NULL);
@@ -7056,6 +7056,9 @@ done: __maybe_unused;
return p;
idle:
+ if (!rf)
+ return NULL;
+
new_tasks = newidle_balance(rq, rf);
/*
diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 1b65a4c3683e..7ece8e820b5d 100644
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -388,7 +388,9 @@ pick_next_task_idle(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
{
struct task_struct *next = rq->idle;
- put_prev_task(rq, prev);
+ if (prev)
+ put_prev_task(rq, prev);
+
set_next_task_idle(rq, next);
return next;
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index 51ee87c5a28a..79f2e60516ef 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -1554,38 +1554,11 @@ pick_next_task_rt(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
struct task_struct *p;
struct rt_rq *rt_rq = &rq->rt;
- if (need_pull_rt_task(rq, prev)) {
- /*
- * This is OK, because current is on_cpu, which avoids it being
- * picked for load-balance and preemption/IRQs are still
- * disabled avoiding further scheduler activity on it and we're
- * being very careful to re-start the picking loop.
- */
- rq_unpin_lock(rq, rf);
- pull_rt_task(rq);
- rq_repin_lock(rq, rf);
- /*
- * pull_rt_task() can drop (and re-acquire) rq->lock; this
- * means a dl or stop task can slip in, in which case we need
- * to re-start task selection.
- */
- if (unlikely((rq->stop && task_on_rq_queued(rq->stop)) ||
- rq->dl.dl_nr_running))
- return RETRY_TASK;
- }
-
- /*
- * We may dequeue prev's rt_rq in put_prev_task().
- * So, we update time before rt_queued check.
- */
- if (prev->sched_class == &rt_sched_class)
- update_curr_rt(rq);
+ WARN_ON_ONCE(prev || rf);
if (!rt_rq->rt_queued)
return NULL;
- put_prev_task(rq, prev);
-
p = _pick_next_task_rt(rq);
set_next_task_rt(rq, p);
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 4cbe2bef92e4..460dd04e76af 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1665,12 +1665,15 @@ struct sched_class {
void (*check_preempt_curr)(struct rq *rq, struct task_struct *p, int flags);
/*
- * It is the responsibility of the pick_next_task() method that will
- * return the next task to call put_prev_task() on the @prev task or
- * something equivalent.
+ * Both @prev and @rf are optional and may be NULL, in which case the
+ * caller must already have invoked put_prev_task(rq, prev, rf).
*
- * May return RETRY_TASK when it finds a higher prio class has runnable
- * tasks.
+ * Otherwise it is the responsibility of the pick_next_task() to call
+ * put_prev_task() on the @prev task or something equivalent, IFF it
+ * returns a next task.
+ *
+ * In that case (@rf != NULL) it may return RETRY_TASK when it finds a
+ * higher prio class has runnable tasks.
*/
struct task_struct * (*pick_next_task)(struct rq *rq,
struct task_struct *prev,
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 8f414018d5e0..7e1cee4e65b2 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -33,10 +33,11 @@ pick_next_task_stop(struct rq *rq, struct task_struct *prev, struct rq_flags *rf
{
struct task_struct *stop = rq->stop;
+ WARN_ON_ONCE(prev || rf);
+
if (!stop || !task_on_rq_queued(stop))
return NULL;
- put_prev_task(rq, prev);
set_next_task_stop(rq, stop);
return stop;
--
2.17.1
next prev parent reply other threads:[~2019-04-23 16:19 UTC|newest]
Thread overview: 109+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-23 16:18 [RFC PATCH v2 00/17] Core scheduling v2 Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 01/17] stop_machine: Fix stop_cpus_in_progress ordering Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 02/17] sched: Fix kerneldoc comment for ia64_set_curr_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 03/17] sched: Wrap rq::lock access Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 04/17] sched/{rt,deadline}: Fix set_next_task vs pick_next_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 05/17] sched: Add task_struct pointer to sched_class::set_curr_task Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 06/17] sched/fair: Export newidle_balance() Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 07/17] sched: Allow put_prev_task() to drop rq->lock Vineeth Remanan Pillai
2019-04-23 16:18 ` Vineeth Remanan Pillai [this message]
2019-04-23 16:18 ` [RFC PATCH v2 09/17] sched: Introduce sched_class::pick_task() Vineeth Remanan Pillai
2019-04-26 14:02 ` Peter Zijlstra
2019-04-26 16:10 ` Vineeth Remanan Pillai
2019-04-29 5:38 ` Aaron Lu
2019-04-23 16:18 ` [RFC PATCH v2 10/17] sched: Core-wide rq->lock Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks Vineeth Remanan Pillai
2019-04-24 0:08 ` Tim Chen
2019-04-24 20:43 ` Vineeth Remanan Pillai
2019-04-24 22:12 ` Tim Chen
2019-04-25 14:35 ` Phil Auld
2019-05-22 19:52 ` Vineeth Remanan Pillai
2019-04-24 0:17 ` Tim Chen
2019-04-24 20:43 ` Vineeth Remanan Pillai
2019-04-29 3:36 ` Aaron Lu
2019-05-10 13:06 ` Peter Zijlstra
2019-04-29 6:15 ` Aaron Lu
2019-05-01 23:27 ` Tim Chen
2019-05-03 0:06 ` Tim Chen
2019-05-08 15:49 ` Aubrey Li
2019-05-08 18:19 ` Subhra Mazumdar
2019-05-08 18:37 ` Subhra Mazumdar
2019-05-09 0:01 ` Aubrey Li
2019-05-09 0:25 ` Subhra Mazumdar
2019-05-09 1:38 ` Aubrey Li
2019-05-09 2:14 ` Subhra Mazumdar
2019-05-09 15:10 ` Aubrey Li
2019-05-09 17:50 ` Subhra Mazumdar
2019-05-10 0:09 ` Tim Chen
2019-04-23 16:18 ` [RFC PATCH v2 12/17] sched: A quick and dirty cgroup tagging interface Vineeth Remanan Pillai
2019-04-25 14:26 ` Phil Auld
2019-04-26 14:13 ` Peter Zijlstra
2019-04-26 14:19 ` Phil Auld
2019-05-10 15:12 ` Julien Desfossez
2019-04-23 16:18 ` [RFC PATCH v2 13/17] sched: Add core wide task selection and scheduling Vineeth Remanan Pillai
2019-04-29 7:13 ` Aaron Lu
2019-05-18 15:37 ` Aubrey Li
2019-05-20 13:04 ` Phil Auld
2019-05-20 14:04 ` Vineeth Pillai
2019-05-21 8:19 ` Aubrey Li
2019-05-21 13:24 ` Vineeth Pillai
2019-04-23 16:18 ` [RFC PATCH v2 14/17] sched/fair: Add a few assertions Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 15/17] sched: Trivial forced-newidle balancer Vineeth Remanan Pillai
2019-04-23 23:46 ` Aubrey Li
2019-04-24 14:03 ` Vineeth Remanan Pillai
2019-04-24 14:05 ` Vineeth Remanan Pillai
2019-04-23 16:18 ` [RFC PATCH v2 16/17] sched: Wake up sibling if it has something to run Vineeth Remanan Pillai
2019-04-26 15:03 ` Peter Zijlstra
2019-04-29 12:36 ` Julien Desfossez
2019-04-23 16:18 ` [RFC PATCH v2 17/17] sched: Debug bits Vineeth Remanan Pillai
2019-05-17 17:18 ` Aubrey Li
2019-04-23 18:02 ` [RFC PATCH v2 00/17] Core scheduling v2 Phil Auld
2019-04-23 18:45 ` Vineeth Remanan Pillai
2019-04-29 3:53 ` Aaron Lu
2019-05-06 19:39 ` Julien Desfossez
2019-05-08 2:30 ` Aaron Lu
2019-05-08 17:49 ` Julien Desfossez
2019-05-09 2:11 ` Aaron Lu
2019-05-15 21:36 ` Vineeth Remanan Pillai
2019-04-23 23:25 ` Aubrey Li
2019-04-24 11:19 ` Vineeth Remanan Pillai
2019-05-15 21:39 ` Vineeth Remanan Pillai
2019-04-24 13:13 ` Aubrey Li
2019-04-24 14:00 ` Julien Desfossez
2019-04-25 3:15 ` Aubrey Li
2019-04-25 9:55 ` Ingo Molnar
2019-04-25 14:46 ` Mel Gorman
2019-04-25 18:53 ` Ingo Molnar
2019-04-25 18:59 ` Thomas Gleixner
2019-04-25 19:34 ` Ingo Molnar
2019-04-25 21:31 ` Mel Gorman
2019-04-26 8:42 ` Ingo Molnar
2019-04-26 10:43 ` Mel Gorman
2019-04-26 18:37 ` Subhra Mazumdar
2019-04-26 19:49 ` Mel Gorman
2019-04-26 9:45 ` Ingo Molnar
2019-04-26 10:19 ` Mel Gorman
2019-04-27 9:06 ` Ingo Molnar
2019-04-26 9:51 ` Ingo Molnar
2019-04-26 14:15 ` Phil Auld
2019-04-26 2:18 ` Aubrey Li
2019-04-26 9:51 ` Ingo Molnar
2019-04-27 3:51 ` Aubrey Li
2019-04-27 9:17 ` Ingo Molnar
2019-04-27 14:04 ` Aubrey Li
2019-04-27 14:21 ` Ingo Molnar
2019-04-27 15:54 ` Aubrey Li
2019-04-28 9:33 ` Ingo Molnar
2019-04-28 10:29 ` Aubrey Li
2019-04-28 12:17 ` Ingo Molnar
2019-04-29 2:17 ` Li, Aubrey
2019-04-29 6:14 ` Ingo Molnar
2019-04-29 13:25 ` Li, Aubrey
2019-04-29 15:39 ` Phil Auld
2019-04-30 1:24 ` Aubrey Li
2019-04-29 16:00 ` Ingo Molnar
2019-04-30 1:34 ` Aubrey Li
2019-04-30 4:42 ` Ingo Molnar
2019-05-18 0:58 ` Li, Aubrey
2019-05-18 1:08 ` Li, Aubrey
2019-04-25 14:36 ` Julien Desfossez
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