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Fri, 21 Nov 2025 04:40:20 GMT Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id C59BF2004E; Fri, 21 Nov 2025 04:40:20 +0000 (GMT) Received: from smtpav02.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 13CB620043; Fri, 21 Nov 2025 04:40:17 +0000 (GMT) Received: from [9.124.217.15] (unknown [9.124.217.15]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 21 Nov 2025 04:40:16 +0000 (GMT) Message-ID: <08ff261e-7ac8-4a1d-bceb-b1bf792171ae@linux.ibm.com> Date: Fri, 21 Nov 2025 10:10:16 +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 09/17] sched/core: Add support for nohz_full CPUs To: K Prateek Nayak , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Cc: mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, tglx@linutronix.de, yury.norov@gmail.com, maddy@linux.ibm.com, srikar@linux.ibm.com, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, iii@linux.ibm.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, christophe.leroy@csgroup.eu References: <20251119124449.1149616-1-sshegde@linux.ibm.com> <20251119124449.1149616-10-sshegde@linux.ibm.com> <0f9ed7ce-3839-4d2b-98b3-25cc4045aa22@amd.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: <0f9ed7ce-3839-4d2b-98b3-25cc4045aa22@amd.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Authority-Analysis: v=2.4 cv=C/nkCAP+ c=1 sm=1 tr=0 ts=691fed3a cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=VkNPw1HP01LnGYTKEx00:22 a=peo6C5Bk6qtxJPoZQsAA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: LMoe7tVnUK2YG5YNYqQVp8mS0YE_L1WW X-Proofpoint-ORIG-GUID: GhJVg2APiqwAyA_Qg4ehK3vnBimoTG0j X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfXy/Od22Cii+Rg q8gswT5ZSRkuWv+urESytqleNCVO8tANdZP+WzNVUs7DEmbN2+cS0N+drmo1eAXJbsQCXz4BAlx 0QK+n7I0Eze8Ss/UeA6e4jnhOS0roQB+HqSLefDgmL8zDyIbdVzWrATKvTD4kiR1gz3urIplM2g SGtQjSq9y1Ve0zHRwtvYkWmLFSZoFEKtiCyYxrIeuzi+XT4xZpdeaIP4DIdQ7tRLt5ds2XY19sh EgRkmBpjLy206QI8krr6C2oLYkWQmvekZDLwfv+z+c1OPbFIbFnz/V/NZnfJuqymELDg10xrN3r ftmUF9Ch57bxlHoJiti5oj2Tdf8wUfEcE92bSQM/HqiSfCPANb9WItIoyWl+xgxMlf0Gfu7sLeO ezgSrMdV0ps+uS9lIv61PLH3CoGwCA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-11-21_01,2025-11-20_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 spamscore=0 impostorscore=0 bulkscore=0 malwarescore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2511150032 Hi Prateek. On 11/21/25 8:46 AM, K Prateek Nayak wrote: > Hello Shrikanth, > > On 11/19/2025 6:14 PM, Shrikanth Hegde wrote: >> Enable tick on nohz full CPU when it is marked as paravirt. >> If there in no CFS/RT running there, disable the tick to save the power. > > Wouldn't the task be pinned if it is running on a nohz CPU? > We don't push out pinned tasks so this seems unnecessary. > Am I missing something? > No. Task will not be pinned if it running on nohz_full unless user has done a taskset. They are still part of sched domains. Pinning is usually true for isolcpus. You need to explicity set taskset for isolcpus since by default you won't go to those CPUs. on nohz_full it is just that tick will be disabled when it has only one task running. If there are more task on it, tick will be enabled and load balancing can run. Example: ( i have 300-479 as nohz_full) taskset -c 300-315 stress-ng --cpu=2 (it was initially on 301,302) 10:27:37 PM 301 100.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10:27:37 PM 302 100.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Ran hackbench for a brief time. After hackbench completes, (it runs now on 301,314) 10:27:43 PM 301 100.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 10:27:43 PM 314 100.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00