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Thu, 18 Jun 2026 04:44:20 +0000 (GMT) Received: from [9.123.5.233] (unknown [9.123.5.233]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 18 Jun 2026 04:44:19 +0000 (GMT) Message-ID: <834b0300-2e5f-41dd-9b2d-2056256c1fdd@linux.ibm.com> Date: Thu, 18 Jun 2026 10:14:19 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 14/20] sched/core: Introduce a simple steal monitor To: Yury Norov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, kprateek.nayak@amd.com, iii@linux.ibm.com, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.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, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org References: <20260617174139.155540-1-sshegde@linux.ibm.com> <20260617174139.155540-15-sshegde@linux.ibm.com> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-Spam-Info: AW1haW4tMjYwNjE4MDAzNSBTYWx0ZWRfX2nH09gCrgAxp Yd1vg5TfjkmdbeVIpny9EtEzQk3D8e9BRYnpoX8fBlgpXBi3YDATBjchzYACI5pQwWcVTd731IT 0X5WXTFE3OLTbODusbrsq2mke7v7ndE= X-Proofpoint-GUID: kHZamUVUo3-LdsA4X7dKJ788HsqMeWAo X-Authority-Analysis: v=2.4 cv=bMgm5v+Z c=1 sm=1 tr=0 ts=6a3377af cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=yicrcqZ2yowHrt1HRdsA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: L8uPRUOKPP_skk8tt93QolJBsljDGIIj X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjE4MDAzNSBTYWx0ZWRfX6IJIzFypPPqA PrKkaJxLE4Nb3rXWztow8uRJqSrwRLnchTT/ZRLNQia6cor2MtXGQ8ey3tk8h31tDmqTxrJ+ZrV xhmTur1E2ijCHF0PmuSqmCFtLoE7c04dKqdvisKI7lbiKPSRXfysF6RF6FCijNoZ/jE3rAxSRrn WTtyJXT6sRDqKb+kgcdnGyi+lIHTKh83pfUjjkmucnDzHnnScLSJUOpXOwexCqOfPvkSfbszHbp svIH/Ho2OZAH1YTnkQ6zm6Zer1WSkcV9G9YRF9SjO4efV6vs9/ak5yAjRLXDWlGiwHaocN6FlVS EhCiQlC8RwM/vKi8umBbj/00rXHrmneuNcJ9K46n6YMot5zU82WVZeWHlHPfidY6KBPkELldn71 dY5EEEbNMJ7I4i+uRBhZGIxsCPPZ/CsF9lVVevGFZDcQgI6yz7DOxp/TF+gyXxBpH/eZSlfuY+c R9kEUUKj6LpAMA4gCfg== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-06-17_02,2026-06-17_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 impostorscore=0 malwarescore=0 adultscore=0 spamscore=0 bulkscore=0 priorityscore=1501 phishscore=0 clxscore=1015 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606180035 On 6/18/26 10:00 AM, Yury Norov wrote: > On Wed, Jun 17, 2026 at 11:11:33PM +0530, Shrikanth Hegde wrote: >> Start with a simple steal monitor. >> >> It is meant to look at steal time and make the decision to >> reduce/increase the preferred CPUs. >> >> It has >> - work function to execute the steal time calculations and decision >> making periodically. >> - low and high thresholds for steal time. >> - sampling period to control the frequency of steal time calculations. >> - cache the previous decision to avoid oscillations > > This monitor is the one implementation out of quite many possible, > right? I don't think it should live in the core scheduler files, it > should be a module. You mean similar to drivers/cpuidle/? a new one drivers/steal_monitor/ ? > >> Signed-off-by: Shrikanth Hegde >> --- >> v3->v4: >> - Drop tmp_mask >> >> include/linux/sched.h | 11 +++++++++++ >> kernel/sched/core.c | 23 +++++++++++++++++++++++ >> kernel/sched/sched.h | 3 +++ >> 3 files changed, 37 insertions(+) >> >> diff --git a/include/linux/sched.h b/include/linux/sched.h >> index 5f523782ca28..ce6bc8a22eb1 100644 >> --- a/include/linux/sched.h >> +++ b/include/linux/sched.h >> @@ -2517,4 +2517,15 @@ extern void migrate_enable(void); >> >> DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable()) >> >> +#ifdef CONFIG_PREFERRED_CPU >> +struct steal_monitor_t { >> + struct work_struct work; >> + ktime_t prev_time; >> + u64 prev_steal; >> + int previous_decision; >> + unsigned int low_threshold; >> + unsigned int high_threshold; >> + unsigned int sampling_period_ms; >> +}; >> +#endif >> #endif >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 24d4abc74241..cc48632dd42d 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -9138,6 +9138,8 @@ void __init sched_init(void) >> >> preempt_dynamic_init(); >> >> + sched_init_steal_monitor(); >> + >> scheduler_running = 1; >> } >> >> @@ -11384,4 +11386,25 @@ void sched_push_current_non_preferred_cpu(struct rq *rq) >> stop_one_cpu_nowait(rq->cpu, sched_non_preferred_cpu_push_stop, >> push_task, this_cpu_ptr(&npc_push_task_work)); >> } >> + >> +struct steal_monitor_t steal_mon; >> + >> +void sched_init_steal_monitor(void) >> +{ >> + INIT_WORK(&steal_mon.work, sched_steal_detection_work); >> + steal_mon.low_threshold = 200; /* 2% steal time */ >> + steal_mon.high_threshold = 500; /* 5% steal time */ >> + steal_mon.sampling_period_ms = 1000; /* once per second */ >> +} >> + >> +/* This is only a skeleton. Subsequent patches introduce more of it */ >> +void sched_steal_detection_work(struct work_struct *work) >> +{ >> + struct steal_monitor_t *sm = container_of(work, struct steal_monitor_t, work); >> + ktime_t now; >> + >> + /* Update the prev_time for next iteration*/ >> + now = ktime_get(); >> + sm->prev_time = now; >> +} >> #endif >> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h >> index 9cb006c21090..984da3827f19 100644 >> --- a/kernel/sched/sched.h >> +++ b/kernel/sched/sched.h >> @@ -4240,8 +4240,11 @@ static inline bool task_has_preferred_cpus(struct task_struct *p) >> #ifdef CONFIG_PREFERRED_CPU >> DECLARE_STATIC_KEY_FALSE(__sched_sm_enable); >> >> +void sched_init_steal_monitor(void); >> +void sched_steal_detection_work(struct work_struct *work); >> void sched_push_current_non_preferred_cpu(struct rq *rq); >> #else /* !CONFIG_PREFERRED_CPU */ >> static inline void sched_push_current_non_preferred_cpu(struct rq *rq) { } >> +static inline void sched_init_steal_monitor(void) { } >> #endif >> #endif /* _KERNEL_SCHED_SCHED_H */ >> -- >> 2.47.3