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Tue, 13 Feb 2024 05:56:02 +0000 Received: from CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::91b3:fd53:a6ee:8685]) by CO6PR10MB5409.namprd10.prod.outlook.com ([fe80::91b3:fd53:a6ee:8685%4]) with mapi id 15.20.7270.036; Tue, 13 Feb 2024 05:56:02 +0000 From: Ankur Arora To: linux-kernel@vger.kernel.org Cc: tglx@linutronix.de, peterz@infradead.org, torvalds@linux-foundation.org, paulmck@kernel.org, akpm@linux-foundation.org, luto@kernel.org, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, willy@infradead.org, mgorman@suse.de, jpoimboe@kernel.org, mark.rutland@arm.com, jgross@suse.com, andrew.cooper3@citrix.com, bristot@kernel.org, mathieu.desnoyers@efficios.com, geert@linux-m68k.org, glaubitz@physik.fu-berlin.de, anton.ivanov@cambridgegreys.com, mattst88@gmail.com, krypton@ulrich-teichert.org, rostedt@goodmis.org, David.Laight@ACULAB.COM, richard@nod.at, mjguzik@gmail.com, jon.grimm@amd.com, bharata@amd.com, raghavendra.kt@amd.com, boris.ostrovsky@oracle.com, konrad.wilk@oracle.com, Ankur Arora Subject: [PATCH 09/30] sched: __schedule_loop() doesn't need to check for need_resched_lazy() Date: Mon, 12 Feb 2024 21:55:33 -0800 Message-Id: <20240213055554.1802415-10-ankur.a.arora@oracle.com> X-Mailer: git-send-email 2.31.1 In-Reply-To: <20240213055554.1802415-1-ankur.a.arora@oracle.com> References: <20240213055554.1802415-1-ankur.a.arora@oracle.com> X-ClientProxiedBy: MW4P221CA0025.NAMP221.PROD.OUTLOOK.COM (2603:10b6:303:8b::30) To CO6PR10MB5409.namprd10.prod.outlook.com (2603:10b6:5:357::14) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: CO6PR10MB5409:EE_|CO1PR10MB4642:EE_ X-MS-Office365-Filtering-Correlation-Id: a1edaddc-6855-4a5b-e3ea-08dc2c587585 X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; 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Explicitly note that we don't need to check for need_resched_lazy() since that only needs to be handled at exit-to-user. Also update the comment above __schedule() to describe TIF_NEED_RESCHED_LAZY semantics. Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Originally-by: Thomas Gleixner Link: https://lore.kernel.org/lkml/87jzshhexi.ffs@tglx/ Signed-off-by: Ankur Arora --- kernel/sched/core.c | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 41c3bd49a700..8e492d20021c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6573,18 +6573,21 @@ pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf) * * 1. Explicit blocking: mutex, semaphore, waitqueue, etc. * - * 2. TIF_NEED_RESCHED flag is checked on interrupt and userspace return - * paths. For example, see arch/x86/entry_64.S. + * 2. TIF_NEED_RESCHED flag is checked on interrupt and TIF_NEED_RESCHED[_LAZY] + * flags on userspace return paths. For example, see kernel/entry/common.c * - * To drive preemption between tasks, the scheduler sets the flag in timer - * interrupt handler scheduler_tick(). + * To drive preemption between tasks, the scheduler sets one of the need- + * resched flags in the timer interrupt handler scheduler_tick(): + * - !CONFIG_PREEMPT_AUTO: TIF_NEED_RESCHED. + * - CONFIG_PREEMPT_AUTO: TIF_NEED_RESCHED or TIF_NEED_RESCHED_LAZY + * depending on the preemption model. * * 3. Wakeups don't really cause entry into schedule(). They add a * task to the run-queue and that's it. * * Now, if the new task added to the run-queue preempts the current - * task, then the wakeup sets TIF_NEED_RESCHED and schedule() gets - * called on the nearest possible occasion: + * task, then the wakeup sets TIF_NEED_RESCHED[_LAZY] and schedule() + * gets called on the nearest possible occasion: * * - If the kernel is preemptible (CONFIG_PREEMPTION=y): * @@ -6802,6 +6805,11 @@ static __always_inline void __schedule_loop(unsigned int sched_mode) preempt_disable(); __schedule(sched_mode); sched_preempt_enable_no_resched(); + + /* + * We don't check for need_resched_lazy() here, since it is + * always handled at exit-to-user. + */ } while (need_resched()); } @@ -6907,7 +6915,7 @@ static void __sched notrace preempt_schedule_common(void) preempt_enable_no_resched_notrace(); /* - * Check again in case we missed a preemption opportunity + * Check again in case we missed an eager preemption opportunity * between schedule and now. */ } while (need_resched());