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Thu, 24 Jul 2025 16:16:28 +0000 From: Prakash Sangappa To: linux-kernel@vger.kernel.org Cc: peterz@infradead.org, rostedt@goodmis.org, mathieu.desnoyers@efficios.com, tglx@linutronix.de, bigeasy@linutronix.de, kprateek.nayak@amd.com, vineethr@linux.ibm.com, prakash.sangappa@oracle.com Subject: [PATCH V7 02/11] sched: Indicate if thread got rescheduled Date: Thu, 24 Jul 2025 16:16:16 +0000 Message-ID: <20250724161625.2360309-3-prakash.sangappa@oracle.com> X-Mailer: git-send-email 2.43.5 In-Reply-To: <20250724161625.2360309-1-prakash.sangappa@oracle.com> References: <20250724161625.2360309-1-prakash.sangappa@oracle.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1099,Hydra:6.1.9,FMLib:17.12.80.40 definitions=2025-07-24_02,2025-07-24_01,2025-03-28_01 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 spamscore=0 adultscore=0 bulkscore=0 suspectscore=0 mlxscore=0 phishscore=0 mlxlogscore=999 malwarescore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2505160000 definitions=main-2507240123 X-Proofpoint-GUID: okQISYXcqNSms0cwarjsW-q8YBYkaaum X-Proofpoint-ORIG-GUID: okQISYXcqNSms0cwarjsW-q8YBYkaaum X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUwNzI0MDEyMyBTYWx0ZWRfXzgggtzVlg266 wiJJf6O+zUuzvDuy+acMThAOmQaG2bSbyHfsb13tLz279fNjGQxQi5tFggfWJkSgjq5jwPOI1yy OkyFv3YmQ/Gb/sqIqxVJujt+pb1xJO60TSlADAGDkd2XAj9l1cIpznICDwM6PedunSyztcGol54 AiwF92ZNrVifkV+kJXl9kM2NILvOkeqnYisGyswxfmCSUKd0Lvm1nzxHWzkLeagCAtnQakMXhHD 19L3v2jWu0ByYDteh86MpK/0fIHhmIR6rwpWpkf8Se1LPLMZeF+Aa7eZxrzdafCtGdYxL/aJyHm kwUyrve2lr9BjUrLVQTR64YPQMIhrqn1r7uLdE9bGDok23pdC3G5yXqlCG8ZRb6k6va11XYCrWB P3sKffqODxkjufcqo+CL+/9VLmpWzKhFios7s6HOL0c6hCOJvUGz3wo1/IWfQLLukgfgMepQ X-Authority-Analysis: v=2.4 cv=IPoCChvG c=1 sm=1 tr=0 ts=68825c5d b=1 cx=c_pps a=zPCbziy225d3KhSqZt3L1A==:117 a=zPCbziy225d3KhSqZt3L1A==:17 a=Wb1JkmetP80A:10 a=yPCof4ZbAAAA:8 a=NiUtxhHkKI-ILPi3m6QA:9 cc=ntf awl=host:12061 Use a bit in rseq flags to indicate if the thread got rescheduled after the cpu time extension was graned. The user thread can check this flag before calling sched_yield() to yield the cpu. Signed-off-by: Prakash Sangappa --- include/linux/sched.h | 2 ++ include/uapi/linux/rseq.h | 10 ++++++++++ kernel/rseq.c | 13 +++++++++++++ kernel/sched/core.c | 5 ++--- 4 files changed, 27 insertions(+), 3 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 5d2819afd481..5df055f2dd9e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -2258,6 +2258,7 @@ unsigned long sched_cpu_util(int cpu); extern bool __rseq_delay_resched(void); extern void rseq_delay_resched_arm_timer(void); extern void rseq_delay_resched_tick(void); +extern void rseq_delay_resched_clear(struct task_struct *tsk); static inline bool rseq_delay_set_need_resched(void) { if (current->rseq_delay_resched == RSEQ_RESCHED_DELAY_REQUESTED) { @@ -2271,6 +2272,7 @@ static inline bool __rseq_delay_resched(void) { return false; } static inline void rseq_delay_resched_arm_timer(void) { } static inline void rseq_delay_resched_tick(void) { } static inline bool rseq_delay_set_need_resched(void) { return false; } +static inline void rseq_delay_resched_clear(struct task_struct *tsk) { } #endif #ifdef CONFIG_SCHED_CORE diff --git a/include/uapi/linux/rseq.h b/include/uapi/linux/rseq.h index 25fc636b17d5..f4813d931387 100644 --- a/include/uapi/linux/rseq.h +++ b/include/uapi/linux/rseq.h @@ -27,6 +27,7 @@ enum rseq_cs_flags_bit { RSEQ_CS_FLAG_NO_RESTART_ON_SIGNAL_BIT = 1, RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT = 2, RSEQ_CS_FLAG_DELAY_RESCHED_BIT = 3, + RSEQ_CS_FLAG_RESCHEDULED_BIT = 4, }; enum rseq_cs_flags { @@ -38,6 +39,9 @@ enum rseq_cs_flags { (1U << RSEQ_CS_FLAG_NO_RESTART_ON_MIGRATE_BIT), RSEQ_CS_FLAG_DELAY_RESCHED = (1U << RSEQ_CS_FLAG_DELAY_RESCHED_BIT), + RSEQ_CS_FLAG_RESCHEDULED = + (1U << RSEQ_CS_FLAG_RESCHEDULED_BIT), + }; /* @@ -135,6 +139,12 @@ struct rseq { * Request by user thread to delay preemption. With use * of a timer, kernel grants extra cpu time upto 30us for this * thread before being rescheduled. + * - RSEQ_CS_FLAG_RESCHEDULED + * Set by kernel if the thread was rescheduled in the extra time + * granted due to request RSEQ_CS_DELAY_RESCHED. This bit is + * checked by the thread before calling sched_yield() to yield + * cpu. User thread sets this bit to 0, when setting + * RSEQ_CS_DELAY_RESCHED to request preemption delay. */ __u32 flags; diff --git a/kernel/rseq.c b/kernel/rseq.c index 8b6af4e12142..6331b653b402 100644 --- a/kernel/rseq.c +++ b/kernel/rseq.c @@ -480,6 +480,19 @@ void rseq_delay_resched_tick(void) if (current->rseq_delay_resched == RSEQ_RESCHED_DELAY_REQUESTED) set_tsk_need_resched(current); } + +void rseq_delay_resched_clear(struct task_struct *tsk) +{ + u32 flags; + + if (tsk->rseq_delay_resched == RSEQ_RESCHED_DELAY_REQUESTED) { + tsk->rseq_delay_resched = RSEQ_RESCHED_DELAY_PROBE; + if (copy_from_user_nofault(&flags, &tsk->rseq->flags, sizeof(flags))) + return; + flags |= RSEQ_CS_FLAG_RESCHEDULED; + copy_to_user_nofault(&tsk->rseq->flags, &flags, sizeof(flags)); + } +} #endif /* CONFIG_RSEQ_RESCHED_DELAY */ #ifdef CONFIG_DEBUG_RSEQ diff --git a/kernel/sched/core.c b/kernel/sched/core.c index e75ecbb2c1f7..ba1e4f6981cd 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -6752,9 +6752,8 @@ static void __sched notrace __schedule(int sched_mode) picked: clear_tsk_need_resched(prev); clear_preempt_need_resched(); - if (IS_ENABLED(CONFIG_RSEQ_RESCHED_DELAY) && - prev->rseq_delay_resched == RSEQ_RESCHED_DELAY_REQUESTED) - prev->rseq_delay_resched = RSEQ_RESCHED_DELAY_PROBE; + if(IS_ENABLED(CONFIG_RSEQ_RESCHED_DELAY)) + rseq_delay_resched_clear(prev); rq->last_seen_need_resched_ns = 0; is_switch = prev != next; -- 2.43.5