Received-SPF: pass (google.com: domain of linux-kernel+bounces-191578-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
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>,
        Daniel Bristot de Oliveira <bristot@kernel.org>
Subject: [PATCH v2 33/35] osnoise: handle quiescent states for PREEMPT_RCU=n, PREEMPTION=y
Date: Mon, 27 May 2024 17:35:19 -0700
Message-Id: <20240528003521.979836-34-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?+a086Osm1ae12R0HP/F5Wv1tfnEY2L0+zKa9mOBdtWVY/vJF/ZBDX1nArCA5?=
 =?us-ascii?Q?pv2++hfSjhGjsWKozC0axk5ERkqy8GnEv8kO/ZWM5O6yzC+zIJuUQ81+2pFl?=
 =?us-ascii?Q?Bq5yEjbiwDn2mOonsOcUZ/cINzDkSBNBrBsXsu85twK5A8USZhQSI7XNA4kt?=
 =?us-ascii?Q?5u96CJYLTaxGZnxQDmwCnzbvkRidpEgw6xRXmbauGWhvrD/UMY0JysCAe4kN?=
 =?us-ascii?Q?9ABb7mZAy4RmSjQdLEya8ZDPtMUI5X95NEFFfsmcBoyuBmo9IJaLw4FtXRn3?=
 =?us-ascii?Q?Di8UfR0eGX5HbWDEHx6gsvE/R2UrZqw35YKzC+Bk4ckQp4IUma1IjbqUGlgB?=
 =?us-ascii?Q?II6tRHDjWWpFV5ZKQS/XJ4r2+QCH/Q4103nbY+L3N5xdZTHMotAYVwJXwOh9?=
 =?us-ascii?Q?owPc8X1WQxXawuxSdC7pFzsy9TVLgqEm7HXgySFBMKHwQwLIyqoF+z3o8B6P?=
 =?us-ascii?Q?zwZymdb9LrP+NdS/Y8vzq5+h6bo0NS7CxCHwNpgVTRLWnG2capYMqtO13pxv?=
 =?us-ascii?Q?v78BQtDZz10vrVYilHH0gCF6sdEGDZew43VcBR63hOubTstlvOC/AYGKNzmn?=
 =?us-ascii?Q?UAfcEc7QWMcZWVcZI75pVOTeai0OZ20ycz6wAPpPl2AZcktQUF4/F+b+9u6F?=
 =?us-ascii?Q?qxyiUjEkWDJ8VtpbfhczHZxy6N7x9j2z7Wdd9LFQVYwrp8eKl5Vjr2xzq0pe?=
 =?us-ascii?Q?ak+o3tIj2cvDARjuoOwfF6r0M2OV4AmWUuIvu4CWcyy/C9/ePDU3vEdE9w+E?=
 =?us-ascii?Q?W1WDFep3PnNEK/sZ+tSgIVZg7KC1tBNHMFN0wJWg7bJ97mPLXqGyohSiKmUV?=
 =?us-ascii?Q?E2nbzIoRbRrMPiPr8h/d3j8LMBI31mIlYybwLdtA9Yvn9ZKJw3E+wDgMUvSD?=
 =?us-ascii?Q?IIHofvXiTiJbt70XY65PLB3QYylXinI6g952Bhgnri4nHUXqufrXOhSRy4GC?=
 =?us-ascii?Q?DuzdsIBOaj/vat7nrHbwZbcGLC0OR73U1HQsrS7GI3s55/8AWjB7EbCEJjjQ?=
 =?us-ascii?Q?UMkD9EEQIBq9eCGYEDU7oJT7g6PyZHLY6Hejq4LqkuXNu9T5vtzbms6GPo2Y?=
 =?us-ascii?Q?8NOmOjHId1JvSYlIsWQ2YsgOzJIHXZwH2VRm4g+two61o/aDH0JRocQ5KyOL?=
 =?us-ascii?Q?dFbEBRPApgUMTQKvUjXt5pCsX5Vfj5Frl5iFN0xbpswD8SPozv18Py4f/2SC?=
 =?us-ascii?Q?iKZSqj6weV/Nh46jsS5bSZK6ZxWZcpczNuJ7XmXdGU0xrADLa80I6uhkC0wX?=
 =?us-ascii?Q?dFNBj+jP0ZUiqWpdP0h8U6VHcuR9x+ZoTVdOnwi9GBqVjwo5U3AjRlNGAyuv?=
 =?us-ascii?Q?33Cqng/hBUBRxfGEfGwT/4dvH/m2/QQaXmqWqD9wZmV5bitrOuR5B9nsOtN9?=
 =?us-ascii?Q?p3bozQuFJ8XsSkcv+a71bohDOHyKZQGjrUst/HML1iPYMipNQz2K8LSxaJWm?=
 =?us-ascii?Q?T6HiZ2OOitYEpeRbhuk7PZz55GSV75KpI4QtpgOsKmUVxMbM6mW33tpMMTyu?=
 =?us-ascii?Q?rsh/gTU6qon5OcO2kt92PnTfr6NSgmdIm/t61ecyekhbeg4zUzuakqqZwe7w?=
 =?us-ascii?Q?m1Ea3bqZPO16WGG7Bww2NXF2dp05rUhHPk0EK97fqC6EDSJRsQYE5DyhOkI8?=
 =?us-ascii?Q?rA=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: 4f91236e-ae1a-40ec-3b14-08dc7eae4baf
X-MS-Exchange-CrossTenant-AuthSource: CO6PR10MB5409.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2024 00:37:04.0135
 (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: dsqwZ4EJaVZHsDlFcEBA8qdYvo9Dh/dpBgN7lWuXR+W0SqwmUu0zBdR1uMHwjMcp9Uh1HcRcSY2E8sokM4ZPEiNWR2Obm5PV+qVbcYS5Lvk=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BN0PR10MB5077
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 bulkscore=0 malwarescore=0 mlxscore=0
 mlxlogscore=999 phishscore=0 spamscore=0 adultscore=0 suspectscore=0
 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2405010000
 definitions=main-2405280003
X-Proofpoint-ORIG-GUID: sLXRKT8sgn5yfogNLaS4xwIllEpBRT57
X-Proofpoint-GUID: sLXRKT8sgn5yfogNLaS4xwIllEpBRT57

To reduce RCU noise for nohz_full configurations, osnoise depends
on cond_resched() providing quiescent states for PREEMPT_RCU=n
configurations. And, for PREEMPT_RCU=y configurations does this
by directly calling rcu_momentary_dyntick_idle().

With PREEMPT_AUTO=y, however, we can have configurations with
(PREEMPTION=y, PREEMPT_RCU=n), which means neither of the above can
help.

Handle that by fallback to the explicit quiescent states via
rcu_momentary_dyntick_idle().

Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Daniel Bristot de Oliveira <bristot@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Suggested-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com>
---
 kernel/trace/trace_osnoise.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c
index a8e28f9b9271..88d2cd2593c4 100644
--- a/kernel/trace/trace_osnoise.c
+++ b/kernel/trace/trace_osnoise.c
@@ -1532,18 +1532,20 @@ static int run_osnoise(void)
 		/*
 		 * In some cases, notably when running on a nohz_full CPU with
 		 * a stopped tick PREEMPT_RCU has no way to account for QSs.
-		 * This will eventually cause unwarranted noise as PREEMPT_RCU
-		 * will force preemption as the means of ending the current
-		 * grace period. We avoid this problem by calling
-		 * rcu_momentary_dyntick_idle(), which performs a zero duration
-		 * EQS allowing PREEMPT_RCU to end the current grace period.
-		 * This call shouldn't be wrapped inside an RCU critical
-		 * section.
+		 * This will eventually cause unwarranted noise as RCU forces
+		 * preemption as the means of ending the current grace period.
+		 * We avoid this by calling rcu_momentary_dyntick_idle(),
+		 * which performs a zero duration EQS allowing RCU to end the
+		 * current grace period. This call shouldn't be wrapped inside
+		 * an RCU critical section.
 		 *
-		 * Note that in non PREEMPT_RCU kernels QSs are handled through
-		 * cond_resched()
+		 * For non-PREEMPT_RCU kernels with cond_resched() (non-
+		 * PREEMPT_AUTO configurations), QSs are handled through
+		 * cond_resched(). For PREEMPT_AUTO kernels, we fallback to the
+		 * zero duration QS via rcu_momentary_dyntick_idle().
 		 */
-		if (IS_ENABLED(CONFIG_PREEMPT_RCU)) {
+		if (IS_ENABLED(CONFIG_PREEMPT_RCU) ||
+		    (!IS_ENABLED(CONFIG_PREEMPT_RCU) && IS_ENABLED(CONFIG_PREEMPTION))) {
 			if (!disable_irq)
 				local_irq_disable();
 
-- 
2.31.1