Received-SPF: pass (google.com: domain of linux-kernel+bounces-191565-linux.lists.archive=gmail.com@vger.kernel.org designates 139.178.88.99 as permitted sender) client-ip=139.178.88.99;
From: Ankur Arora <ankur.a.arora@oracle.com>
To: linux-kernel@vger.kernel.org
Cc: tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org,
        paulmck@kernel.org, rostedt@goodmis.org, mark.rutland@arm.com,
        juri.lelli@redhat.com, joel@joelfernandes.org, raghavendra.kt@amd.com,
        sshegde@linux.ibm.com, boris.ostrovsky@oracle.com,
        konrad.wilk@oracle.com, Ankur Arora <ankur.a.arora@oracle.com>,
        Ingo Molnar <mingo@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Subject: [PATCH v2 21/35] sched: prepare for lazy rescheduling in resched_curr()
Date: Mon, 27 May 2024 17:35:07 -0700
Message-Id: <20240528003521.979836-22-ankur.a.arora@oracle.com>
In-Reply-To: <20240528003521.979836-1-ankur.a.arora@oracle.com>
References: <20240528003521.979836-1-ankur.a.arora@oracle.com>
Content-Transfer-Encoding: 8bit
Content-Type: text/plain
Precedence: bulk
MIME-Version: 1.0
X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-MessageData-0: 
	=?us-ascii?Q?G/Mvd5OfU4+WeEMChICK8BFGnZiyfvZf9CrP1lzD7MhAU2jk3EuM2gs72H7t?=
 =?us-ascii?Q?VInByyGcad7TAdBCwFOtnKxJnxg+dNghRB2Z9lpu5Rw7bw6VoamfOkc+3FU/?=
 =?us-ascii?Q?cPW7H1ErX/VOLOEIo41dHp6RSVCCxzkoGaX5otgQIq1IwiY3pK/8eAKEZ2Y/?=
 =?us-ascii?Q?DWFLCt6v44x/jFcvD/J55fNNssqqWB+0p1QBKWi1QbkgiZkqGiEP8+QF/oHx?=
 =?us-ascii?Q?jSPci+Q40eEUexKbS7A+k4G/xEUbPFe5Q+dnSd9GWm8hwXKpxu21EwPj0mh3?=
 =?us-ascii?Q?CN3t8VaT9GHXojy+vJVeVOWG6DceoTJNipNlmvErDZwCFMOyYD5GzODOeR0H?=
 =?us-ascii?Q?hIiiNDHh4ZQY9ZDDpKrtGLnf5L8SBk220UEFVh6VfnBy/oHSzf2luN40EAmB?=
 =?us-ascii?Q?0Fx8QfASVeq9APB/+Ov7RZDw0rRodw4HDTx1eNnD0KlMWcE/qZNxNm2KFQfR?=
 =?us-ascii?Q?LcNZ4lOf8vtoPbxv2p10VsvyRMzw/xFRYKwkTd+AjTZI/6OBcxpuTvmOWO3u?=
 =?us-ascii?Q?gfIYxrRzamuzbbOWzYKd5ydYXONnRQiG4N96BvjL7CZOLL84xYdUi4XfYvNO?=
 =?us-ascii?Q?rfwa97NHKhB6n+NtD9HoEmDofObhdjuMkAUOaTG1N9w0CcbkHoMs5DsvFhrE?=
 =?us-ascii?Q?AuI00OHoEB9OKWs3cZp4rnpSw5U0Wn/lNB40eGHcIbTj+jcIfbjfjQeSJLLE?=
 =?us-ascii?Q?c41msq1KORom04r8hePL3LofNl7WUqgD3vTwalwMMSj++c83vG043iJ0d/Nr?=
 =?us-ascii?Q?lIixrXIYx3nAZFSc40i2jsDHF+U5taJyFvJDxIKN5oJ8AH7hR6jKQ67fSJCh?=
 =?us-ascii?Q?FtX6TAm2HDyjqwhUOh/aSH8LjH+5eDacEiRMCG6UyfzTt08ojIQZnZALlzNS?=
 =?us-ascii?Q?KFxN0XyAwsWo8fdQS6c+jRkoq4aRdZ3L8d3zTMc+PC/k0oezFKyZ+RK3gSt2?=
 =?us-ascii?Q?AhK7ori/yUXyvL5n/p3j3mbVJe/e284glqvCJlMjxUZ9taD6TH+uSUC3kx40?=
 =?us-ascii?Q?wUEp0OAhXWgxO1jtTmxDNRNQFDJXAizPh/tb+x0kcxvLCgc/fajs378SJ5fa?=
 =?us-ascii?Q?qN1gxXMmHEwczbwOBs94mjcz6DVXMpOy8BH0yWBK2uHsNMMbX1ediXBEilmG?=
 =?us-ascii?Q?/3PUv6p3JQZ/jByNTAHpMz1SqaJ5R9MO71RgqjXvA9/mYjqDHi0qizOUWhBd?=
 =?us-ascii?Q?lE3o2kH9MJSXzFqINWSOiov0nFQ9OJeQMC7MoKWuNDBFT/0Bs6IyzowO29za?=
 =?us-ascii?Q?iGG/wlsdyWCGzy5sTkFSd3xgSUm6y82o4cYfF9SVVpKGR5b5dNG0ndp0pAk0?=
 =?us-ascii?Q?2cyrUk6tAk3JMtCc2uv6mggKmv5yA7/8mzwoA4gbUE+5bPnxXMyYxefhpQ0r?=
 =?us-ascii?Q?ED2pBOH0KtJV1RsS9TgkXv9VVXf88yhQdsaKvHf77w4A4XkuASSo66XD04H8?=
 =?us-ascii?Q?EVYutSF4rBCMxERlpPmTylqfd4aGptsEII3gp+QPiLCmcXzb0tceHXbGnoOX?=
 =?us-ascii?Q?LmmVX4CL60Ey9O66qnYML1eND0O7RQwaAsV5jYQjSfDy+FX8bSmqJsB57liO?=
 =?us-ascii?Q?rZ4SwUklXaomxKcXFuuudF78jWanx/h38TnuUpUp2EHX4sIzI316OK+TOC6F?=
 =?us-ascii?Q?4Q=3D=3D?=
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-ChunkCount: 1
X-MS-Exchange-AntiSpam-ExternalHop-MessageData-0: 
	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
X-OriginatorOrg: oracle.com
X-MS-Exchange-CrossTenant-Network-Message-Id: db001b31-e4d1-4c11-b09d-08dc7eae381b
X-MS-Exchange-CrossTenant-AuthSource: CO6PR10MB5409.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2024 00:36:31.1563
 (UTC)
X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted
X-MS-Exchange-CrossTenant-Id: 4e2c6054-71cb-48f1-bd6c-3a9705aca71b
X-MS-Exchange-CrossTenant-MailboxType: HOSTED
X-MS-Exchange-CrossTenant-UserPrincipalName: i4z5qVetcSWuQjyczfVmB8DCKHaTsZJOxu9f2ZU/fWFlMOQ91FlMdc8wNYDcG0t6PVBfV6RCPVS0WpXGwBRRMFzHadNy3YXI57yiDxNGmu4=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS7PR10MB7177
X-Proofpoint-Virus-Version: vendor=baseguard
 engine=ICAP:2.0.293,Aquarius:18.0.1039,Hydra:6.0.650,FMLib:17.12.28.16
 definitions=2024-05-27_06,2024-05-27_01,2024-05-17_01
X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxscore=0 spamscore=0 suspectscore=0
 adultscore=0 phishscore=0 malwarescore=0 mlxlogscore=999 bulkscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2405010000
 definitions=main-2405280003
X-Proofpoint-ORIG-GUID: WmDCV3O5eq03Q2rIkM4yb7taqbiTWBkb
X-Proofpoint-GUID: WmDCV3O5eq03Q2rIkM4yb7taqbiTWBkb

Handle RESCHED_LAZY in resched_curr(), by registering an intent to
reschedule at exit-to-user.
Given that the rescheduling is not imminent, skip the preempt folding
and the resched IPI.

Also, update set_nr_and_not_polling() to handle RESCHED_LAZY. Note that
there are no changes to set_nr_if_polling(), since lazy rescheduling
is not meaningful for idle.

And finally, now that there are two need-resched bits, enforce a
priority order while setting them.

Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Originally-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 kernel/sched/core.c | 35 +++++++++++++++++++++++------------
 1 file changed, 23 insertions(+), 12 deletions(-)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index df8e333f2d8b..27b908cc9134 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -899,14 +899,14 @@ static inline void hrtick_rq_init(struct rq *rq)
 
 #if defined(CONFIG_SMP) && defined(TIF_POLLING_NRFLAG)
 /*
- * Atomically set TIF_NEED_RESCHED and test for TIF_POLLING_NRFLAG,
+ * Atomically set TIF_NEED_RESCHED[_LAZY] and test for TIF_POLLING_NRFLAG,
  * this avoids any races wrt polling state changes and thereby avoids
  * spurious IPIs.
  */
-static inline bool set_nr_and_not_polling(struct task_struct *p)
+static inline bool set_nr_and_not_polling(struct task_struct *p, resched_t rs)
 {
 	struct thread_info *ti = task_thread_info(p);
-	return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & _TIF_POLLING_NRFLAG);
+	return !(fetch_or(&ti->flags, _tif_resched(rs)) & _TIF_POLLING_NRFLAG);
 }
 
 /*
@@ -931,9 +931,9 @@ static bool set_nr_if_polling(struct task_struct *p)
 }
 
 #else
-static inline bool set_nr_and_not_polling(struct task_struct *p)
+static inline bool set_nr_and_not_polling(struct task_struct *p, resched_t rs)
 {
-	__set_tsk_need_resched(p, RESCHED_NOW);
+	__set_tsk_need_resched(p, rs);
 	return true;
 }
 
@@ -1041,25 +1041,34 @@ void wake_up_q(struct wake_q_head *head)
 void resched_curr(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
+	resched_t rs = RESCHED_NOW;
 	int cpu;
 
 	lockdep_assert_rq_held(rq);
 
-	if (__test_tsk_need_resched(curr, RESCHED_NOW))
+	/*
+	 * TIF_NEED_RESCHED is the higher priority bit, so if it is already
+	 * set, nothing more to be done.
+	 */
+	if (__test_tsk_need_resched(curr, RESCHED_NOW) ||
+	    (rs == RESCHED_LAZY && __test_tsk_need_resched(curr, RESCHED_LAZY)))
 		return;
 
 	cpu = cpu_of(rq);
 
 	if (cpu == smp_processor_id()) {
-		__set_tsk_need_resched(curr, RESCHED_NOW);
-		set_preempt_need_resched();
+		__set_tsk_need_resched(curr, rs);
+		if (rs == RESCHED_NOW)
+			set_preempt_need_resched();
 		return;
 	}
 
-	if (set_nr_and_not_polling(curr))
-		smp_send_reschedule(cpu);
-	else
+	if (set_nr_and_not_polling(curr, rs)) {
+		if (rs == RESCHED_NOW)
+			smp_send_reschedule(cpu);
+	} else {
 		trace_sched_wake_idle_without_ipi(cpu);
+	}
 }
 
 void resched_cpu(int cpu)
@@ -1154,7 +1163,7 @@ static void wake_up_idle_cpu(int cpu)
 	 * and testing of the above solutions didn't appear to report
 	 * much benefits.
 	 */
-	if (set_nr_and_not_polling(rq->idle))
+	if (set_nr_and_not_polling(rq->idle, RESCHED_NOW))
 		smp_send_reschedule(cpu);
 	else
 		trace_sched_wake_idle_without_ipi(cpu);
@@ -6704,6 +6713,8 @@ static void __sched notrace __schedule(unsigned int sched_mode)
 	}
 
 	next = pick_next_task(rq, prev, &rf);
+
+	/* Clear both TIF_NEED_RESCHED, TIF_NEED_RESCHED_LAZY */
 	clear_tsk_need_resched(prev);
 	clear_preempt_need_resched();
 #ifdef CONFIG_SCHED_DEBUG
-- 
2.31.1