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Fri, 25 Sep 2026 09:16:02 +0000 (GMT) Received: from [9.39.19.124] (unknown [9.39.19.124]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 25 Sep 2026 09:16:02 +0000 (GMT) Message-ID: <3a509e01-6d50-47ed-a53e-2613f2aaee8b@linux.ibm.com> Date: Fri, 25 Sep 2026 14:46:01 +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 v13 06/13] sched/core: Try to use a preferred CPU in is_cpu_allowed To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net, meted@linux.ibm.com, ynorov@nvidia.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, 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, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org, jgross@suse.com, virtualization@lists.linux.dev, sunlightlinux@gmail.com References: <20260909135617.871006-1-sshegde@linux.ibm.com> <20260909135617.871006-7-sshegde@linux.ibm.com> <20260925074314.GF4121339@noisy.programming.kicks-ass.net> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <20260925074314.GF4121339@noisy.programming.kicks-ass.net> 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-ORIG-GUID: YVQjQS8n_el1P8wylsA1uh2GsLa7bi2V X-Proofpoint-Spam-Info: AW1haW4tMjYwOTI1MDAzNiBTYWx0ZWRfX5Wcw4Krc2449 1EmLh5yThqVNqFfjMuzk9yQWQV7qeHekWzDhprSevZ67gYAa6JcThmfc/yxJF3r0gdwDIbTjUwC cYsyF7CpoPiVvvCtWC4P1iRgNXfeCVo= X-Authority-Analysis: v=2.4 cv=FLiOVOos c=1 sm=1 tr=0 ts=6ab63be2 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=LuPJPAu-xtmjmTxlju0A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: xrjdfTOlYSFchly5w9RSXeFp2lHqp4dZ X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTI1MDAzNiBTYWx0ZWRfX1BAoKHzEkdZl chgcqQsEqPipJ4xWe7Z+6ON9gLcm2pfTaEH0oSLNzXpC8rfKSiHt10wU/twwpq51s7WePYkonmU g3xP/zpq+1LXZchR34K10HB03L9loqleW8ZFRj7izGiefFm791hNA7yLbQXzJXinQKEsnxD+33H DfKoVwZhI6+A3JrcNGJkpZ4wOoahiaCuQD36yCpfGZ7RXKGJDPViW0hrb58AWj7w6kKBwWY3h5E gpuB+mK1y1kysTQME9NbK67KIvLAIt6d7c8D2qmOBFxzzEZgoDl1akGkDSp8aD2wog6KUAr4tIS Xt1HeSC0elmDx3Yen+c+9zSYXSn5qtV6FeQwxmbRGoTgawnEI4kGYJDrVUa+IYAdKrWfwLs0Pl0 Roxw3h6fjhX++LBPfLflLq8+Fc8nPzh4G//zhEEu9Tkv04e3Gd2ptnTqfRUdEE4RHOlshyycWB7 nmIWzJRtIw7vDz42CuA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-25_02,2026-09-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 impostorscore=0 phishscore=0 spamscore=0 clxscore=1015 suspectscore=0 bulkscore=0 lowpriorityscore=0 priorityscore=1501 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2609250036 Hi Peter. Thanks for looking into the patches. On 9/25/26 1:13 PM, Peter Zijlstra wrote: > On Wed, Sep 09, 2026 at 07:26:10PM +0530, Shrikanth Hegde wrote: > >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index a689a0cea4eb..b4ef2e92d786 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -2504,6 +2504,23 @@ static inline bool rq_has_pinned_tasks(struct rq *rq) >> return rq->nr_pinned; >> } >> >> +static inline bool task_can_sched_on_preferred(int cpu, struct task_struct *p) > > (somehow those arguments feel backwards) > >> +{ >> + if (cpu_preferred(cpu)) >> + return false; > > FWIW, this reads very weird. task_can_sched_on_preferred() returning > false when task is on a preferred cpu. > How about below signature? static inline bool task_can_migrate_to_preferred(struct task_struct *p, int cpu) > The question really is more like: can we migrate to a preferred CPU, and > in that context it makes more sense. No point in migrating if we are > already on one. > > Perhaps a comment on top of the function can clarify? > Above new function name is self explanatory IMHO. >> + /* Only FAIR tasks honor preferred CPU state */ >> + if (unlikely(p->sched_class != &fair_sched_class)) >> + return false; >> + >> + /* Ignore preferred state if task affinity is changing */ >> + if (unlikely(!cpumask_test_cpu(task_cpu(p), p->cpus_ptr))) >> + return false; >> + >> + return cpumask_intersects_and(p->cpus_ptr, cpu_preferred_mask, >> + task_cpu_possible_mask(p)); >> +}