Received-SPF: pass (google.com: domain of linux-kernel+bounces-191555-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>,
        Andy Lutomirski <luto@kernel.org>
Subject: [PATCH v2 10/35] entry: irqentry_exit only preempts for TIF_NEED_RESCHED
Date: Mon, 27 May 2024 17:34:56 -0700
Message-Id: <20240528003521.979836-11-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?HnmjtQeK88C6TOMg/QPP22BBZEJWJE0pNGcVO5SW2BTgm43d2RR82MLFXS5Z?=
 =?us-ascii?Q?VFr2vSOZKOD7BrdAFIrAH3IHRwNAMqE/50IJ1gNt0Gn7+SS2Cm7bpUE9Eugy?=
 =?us-ascii?Q?MG1jmaJBo2RH+vDEUqPl7O/Kz9yOjKG3OrNCfVpo5DvBKgV+lSZp6Cme9XtJ?=
 =?us-ascii?Q?80k1vMx045U7z9eHdprae0OZWiySuOvB2YRqbx1tdNwIDS2HxL5eaab+jEgD?=
 =?us-ascii?Q?FQMSe7crautMmZcEAiT7HhNfa7LdD64b8cchGruG5k/ySYjwj3uAerK5wcaP?=
 =?us-ascii?Q?Tk0FSjPx8q44TFnLI1jfFVfgRmL0HusZjA9wJUOKCnLAPs2gXgNk3mlpsEU6?=
 =?us-ascii?Q?JTpO4gUzId4HpCTsdCO29wYVCS9FLKwecTfG5mC5fIHTWsxyXh01cqEqSewb?=
 =?us-ascii?Q?LxljnY1Nk1B1Zk+G66JoX0SvVXtSOs8YBRpQQ7wZnQeDIuL/qzE92/yY3jgV?=
 =?us-ascii?Q?2AinuB7NfNlmrGWVintwCu3gDhcwmJINQUaVN5MqAVo3TFL2Eqek/98iYmQZ?=
 =?us-ascii?Q?xAQ2O0FA1tqZO/etTsbuwsZvQGGo6QUK+9LzS4u9dcnb+gga3lhj7uYg3wjr?=
 =?us-ascii?Q?4j4PhhLECIYaTO4kS5GjolFDnfif7WO/8fvm1KLvxO6uVoBWE7TX5WVHfe7y?=
 =?us-ascii?Q?KW9PaPSwbGGE/kH5DC3JVcl0SuzDf6rl9knLYyjydwB3M7OXVTqCTiAfYT2P?=
 =?us-ascii?Q?rpgJySy7YYgFnsCW5lgmSP4t8GMHpx6amMr4NnixBeCtDtx5DUXnkWxsf1+1?=
 =?us-ascii?Q?cDyzs/ReiecS9UYx7tNRO/smNShr+JFPmqj5++EFNuWUeX3RosGJV+h805Ce?=
 =?us-ascii?Q?bIoMv4FIFasnp6fJQOlI+EawaGQ6p7djV8sOqbE4B+klB96yjt8qilpfNRSV?=
 =?us-ascii?Q?4Lp1eTSWVPF5qqjh3bzJTEpiuD6PIK3+9KemJA1x9/9vTjBeWE7VNgaede8F?=
 =?us-ascii?Q?I8TY2df1HOQGAuK4x5hdhri+8MwukYgYLRiQ62rLqhFswKfXZKyRzQaZcGth?=
 =?us-ascii?Q?XlYM+4zfpMhs66ZHVJ+U+BTDg9t1uB/CVzOjfnK8xhRdQs4nBhkCvAsxsRvs?=
 =?us-ascii?Q?9QsLkLWBPYwyw2cf1MFXH5+mqTmNCQr3FtjRzYTRsOiY8Lf/mZRC23rBO7zL?=
 =?us-ascii?Q?f8PR3GaEBD+Q68mx3ir4OWLvUid+Y7hKag3gOnRQHBfjh1xi2TYGho2eOa+Q?=
 =?us-ascii?Q?CaXJ1QJpmwBF8WhLpmt/Kdoc4EuE5mciL2+ZpxUW+60zfnb6IVOrxNuZ0Xc9?=
 =?us-ascii?Q?O7RjtV4NUm6J3rapodyUWJebQjhBALcK3ku/RG2IcnWCOiLnRdlxvb9dLdNX?=
 =?us-ascii?Q?sauUadQTCO8afN6YSzZBrACMjHoNlNjc6dVBbm3wS93SkSSO5LtyVRV95db1?=
 =?us-ascii?Q?1TGepJcJCN6xMF7/cuNHo5kZboEZHcocHmK/kAq62iJmLw7A4g5diGu0ZR+C?=
 =?us-ascii?Q?AFq8/dXhQBrM45vSw/lwILY2lGQtAGfUeutzGflO0Z6TDN6d6cUCl8MFph1w?=
 =?us-ascii?Q?qPHRCG2P8hGdR5NJQcYHnlLORjZtL9k4LGwfKPgBfjKple6WuNz4vEEkszuM?=
 =?us-ascii?Q?PaHqDJGHL/jbfKjt4bY1uiuULeGB54+VAuE79pTMtP0OyWV7mF9ZohBLhlVq?=
 =?us-ascii?Q?vw=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: 1b4b4bf4-b1da-4235-8bce-08dc7eae2523
X-MS-Exchange-CrossTenant-AuthSource: CO6PR10MB5409.namprd10.prod.outlook.com
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-OriginalArrivalTime: 28 May 2024 00:35:59.3117
 (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: rQbUrd4HuaP5uUfz2noagYkczhQHcHSvjEkmaj27457vsSUHsQu9jOOgCWywMBheUMRYvad6SXisJa1sxl6XzfvX00cqRXB0KOPQQRrMcMY=
X-MS-Exchange-Transport-CrossTenantHeadersStamped: MW4PR10MB6510
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 mlxlogscore=999 spamscore=0
 phishscore=0 bulkscore=0 malwarescore=0 adultscore=0 mlxscore=0
 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1
 engine=8.12.0-2405010000 definitions=main-2405280003
X-Proofpoint-GUID: OKVxMMImb3nTxP1BJEIXQmRk5XHcL1-A
X-Proofpoint-ORIG-GUID: OKVxMMImb3nTxP1BJEIXQmRk5XHcL1-A

Use __tif_need_resched(RESCHED_NOW) instead of need_resched() to be
explicit that this path only reschedules if it is needed imminently.

Also, add a comment about why we need a need-resched check here at
all, given that the top level conditional has already checked the
preempt_count().

Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.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/entry/common.c | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index bcb23c866425..c684385921de 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -307,7 +307,16 @@ void raw_irqentry_exit_cond_resched(void)
 		rcu_irq_exit_check_preempt();
 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 			WARN_ON_ONCE(!on_thread_stack());
-		if (need_resched())
+
+		/*
+		 * Check if we need to preempt eagerly.
+		 *
+		 * Note: we need an explicit check here because some
+		 * architectures don't fold TIF_NEED_RESCHED in the
+		 * preempt_count. For archs that do, this is already covered
+		 * in the conditional above.
+		 */
+		if (__tif_need_resched(RESCHED_NOW))
 			preempt_schedule_irq();
 	}
 }
-- 
2.31.1