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Tue, 7 Apr 2026 19:20:31 +0000 (GMT) From: Shrikanth Hegde To: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, yury.norov@gmail.com, gregkh@linuxfoundation.org Cc: sshegde@linux.ibm.com, pbonzini@redhat.com, seanjc@google.com, kprateek.nayak@amd.com, vschneid@redhat.com, iii@linux.ibm.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, mgorman@suse.de, bsegall@google.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, joelagnelf@nvidia.com Subject: [PATCH v2 05/17] sched/core: allow only preferred CPUs in is_cpu_allowed Date: Wed, 8 Apr 2026 00:49:38 +0530 Message-ID: <20260407191950.643549-6-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260407191950.643549-1-sshegde@linux.ibm.com> References: <20260407191950.643549-1-sshegde@linux.ibm.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-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=KeridwYD c=1 sm=1 tr=0 ts=69d55909 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=A5OVakUREuEA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=h5kyaPOYuMV5y32J0wcA:9 X-Proofpoint-ORIG-GUID: MDCX_Hqe7i5wiAV2pk-UGWEJZFfwwR2x X-Proofpoint-GUID: g_CS_MFa98xLqMO4VAueCD47wIj7CfnQ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNDA3MDE3NSBTYWx0ZWRfX58hgDryr/k1B dCeBWobGGwN2aZ2d4jHlGHvJJ9L0Wmv7nM/pN+nKlLfX50DdNz4+CLsx5uahRR71Ag6B1F5pjFn oymCuP4eI3PCQ2AWI3HjiXWfuDGOFOqt7v/fFLMoHapB4umyxBogFGw3SZBE9U/LVtI2aIdIinb PtttJWdgWtJuDoDMwA0x9PVp2+0IPfGucfrHuXrF5Fdr8W9cyUbLSfGG9iXac/lPEWeZs+I2TLh YS19KlXt7siyNLG9siuon+GfLft+Z3sTzBJp3H1QvAhiUUQHD8Q4m3LKeMW6037Na2IovJmC6Iu 6jfK0y4sH7e1ZTAoWxeLD8gOu5nBjODAxUWu9k5KZyTCHCIB2HDo1hrUZ67QJbJwthnVT7lQP36 B0e89vsrk0V95hwGzPuT7v+gBkOqNTmkM9600uyQH7yiybKS0Pkm5h1XNgH42CLTyFPmVeGSIuY 9eXWkKoQLVMhzpbgEYw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-04-07_04,2026-04-07_05,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 malwarescore=0 lowpriorityscore=0 adultscore=0 impostorscore=0 clxscore=1015 phishscore=0 priorityscore=1501 spamscore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604010000 definitions=main-2604070175 When possible, choose a preferred CPUs to pick. Push task mechanism uses stopper thread which going to call select_fallback_rq and use this mechanism to pick only a preferred CPU. When task is affined only to non-preferred CPUs it should continue to run there. Detect that by checking if cpus_ptr and cpu_preferred_mask interesect or not. Signed-off-by: Shrikanth Hegde --- kernel/sched/core.c | 17 ++++++++++++++--- kernel/sched/sched.h | 12 ++++++++++++ 2 files changed, 26 insertions(+), 3 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 7ea05a7a717b..336e7c694eb7 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2463,9 +2463,16 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) if (is_migration_disabled(p)) return cpu_online(cpu); - /* Non kernel threads are not allowed during either online or offline. */ - if (!(p->flags & PF_KTHREAD)) - return cpu_active(cpu); + /* + * Non kernel threads are not allowed during either online or offline. + * Ensure it is a preferred CPU to avoid further contention + */ + if (!(p->flags & PF_KTHREAD)) { + if (!cpu_active(cpu)) + return false; + if (!cpu_preferred(cpu) && task_can_run_on_preferred_cpu(p)) + return false; + } /* KTHREAD_IS_PER_CPU is always allowed. */ if (kthread_is_per_cpu(p)) @@ -2475,6 +2482,10 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu) if (cpu_dying(cpu)) return false; + /* Try on preferred CPU first */ + if (!cpu_preferred(cpu) && task_can_run_on_preferred_cpu(p)) + return false; + /* But are allowed during online. */ return cpu_online(cpu); } diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 88e0c93b9e21..7271af2ca64f 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -4130,4 +4130,16 @@ DEFINE_CLASS_IS_UNCONDITIONAL(sched_change) #include "ext.h" +#ifdef CONFIG_PARAVIRT +static inline bool task_can_run_on_preferred_cpu(struct task_struct *p) +{ + return cpumask_intersects(p->cpus_ptr, cpu_preferred_mask); +} +#else +static inline bool task_can_run_on_preferred_cpu(struct task_struct *p) +{ + return true; +} +#endif + #endif /* _KERNEL_SCHED_SCHED_H */ -- 2.47.3