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Thu, 18 Jun 2026 06:05:19 +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 06:05:19 +0000 (GMT) Message-ID: <58c10d42-f790-4480-9d55-475d561f55b9@linux.ibm.com> Date: Thu, 18 Jun 2026 11:35:18 +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 10/20] sched/core: Push current task from non preferred CPU To: K Prateek Nayak , linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, iii@linux.ibm.com Cc: 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> <20260617174139.155540-11-sshegde@linux.ibm.com> <45ad6ca0-0ce9-4b32-9660-3d4afffca607@amd.com> From: Shrikanth Hegde Content-Language: en-US In-Reply-To: <45ad6ca0-0ce9-4b32-9660-3d4afffca607@amd.com> 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: AW1haW4tMjYwNjE4MDA1MSBTYWx0ZWRfX968R1OEseBDi YNpJqX/SmGtBE4CNypM08UQ+RdauavLAgwqgwJpyLqQPn/uobWZrU31jt79wGdTNQFmyJMv2kzP qsAziaf1t7XlRwQNSmtmb+iL4SnyCrA= X-Proofpoint-GUID: bA7Ogax4TfLrCdl_eHFcVa5UChec-UZk X-Authority-Analysis: v=2.4 cv=bMgm5v+Z c=1 sm=1 tr=0 ts=6a338aaa cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=FelO9ux0wxsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=LpxQHL3P2FQ0YFo1bYUA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: kQyt2kffe42GiqloFA30MIQmOjLSQq4q X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjE4MDA1MSBTYWx0ZWRfXxxYKfni5fsUp /K3IHaR02LSuoTuCgHM9JaTjULW70D3O9752r1ucUL41NusN7Luy0SrVDcmtzn3PM/asc8pWMoC uw5N9imba5U6OdIFf38h01/9kbGYuNjRFZEGtP3FxQNKGARJM9P7E0huJrIwZgrnyYzA04fHotA els505jiHPQlQ9LglTUo5mBe+eHVbbpwXiMB03qNJHfr2/tjLmD7XIYn3pJ8adQJDP3H3BhmimJ bkH2Wq3IoniKCWVAHq6qcij4zFSjeQuhwZSryd4UP9aKHA703fxDNPB/kYdfv4V8kPXUZtIDk6+ EBrv2trILmfTROAjcjQiP5nPnMn8S5PYjsqQHkTTA5Do4n1GyZYxJZsSoXrBoHy/bZcHvMLBjlQ hKMBBaPmMwVwKdvHu4aVl+Z6y23M8AxzN0THiV5omm8EqTnxKPpvTmG6V5V+rvxDWyAhtalzALj bTC1dYjZ9U4MaQBC0kA== 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-2606180051 On 6/18/26 9:39 AM, K Prateek Nayak wrote: > Hello Shrikanth, > > On 6/17/2026 11:11 PM, Shrikanth Hegde wrote: >> +static int sched_non_preferred_cpu_push_stop(void *arg) >> +{ >> + struct task_struct *p = arg; >> + struct rq *rq = this_rq(); >> + struct rq_flags rf; >> + int cpu; >> + >> + /* sanity check */ >> + if (cpu_preferred(rq->cpu)) >> + return 0; > > I think this early return path should also clear "push_task_work_done" > indicator, otherwise, we will fail to schedule the stopper on this CPU > next time. Ok. > > Also, we may need to add a context_unsafe_alias(rq) call here to keep > the context analysis bits happy similar to migration_cpu_stop(). > Let me see that. >> + >> + raw_spin_lock_irq(&p->pi_lock); >> + rq_lock(rq, &rf); >> + rq->push_task_work_done = 0; >> + >> + update_rq_clock(rq); >> + >> + if (task_rq(p) == rq && task_on_rq_queued(p)) { >> + cpu = select_fallback_rq(rq->cpu, p); > > Do we need a task_has_preferred_cpus() sanity check here? > > If the affinity changed before the stopper grabbed the p->pi_lock, and > there are no preferred CPUs to run on anymore, might as well keep the > task here instead of migrating it away. > No I think. If affinity changed before stopper started running, subsequent select_fallback_rq will return the CPU it can run. If it has no choice but a non-preferred CPU, it will return a non-preferred CPU too. >> + rq = __migrate_task(rq, &rf, p, cpu); >> + } >> + >> + rq_unlock(rq, &rf); >> + raw_spin_unlock_irq(&p->pi_lock); >> + put_task_struct(p); >> + >> + return 0; >> +} >