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Tue, 10 Nov 2026 09:15:59 +0000 (GMT) Received: from [9.39.31.79] (unknown [9.39.31.79]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 10 Nov 2026 09:15:59 +0000 (GMT) Message-ID: <1d1b22ce-fdf1-47ad-99ec-8c9925ea7275@linux.ibm.com> Date: Tue, 10 Nov 2026 14:45:58 +0530 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/6] sched: Expose writable interface for preferred CPUs mask To: Maxim Kuvyrkov Cc: Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Juri Lelli , Vincent Guittot , Yury Norov , "Rafael J. Wysocki" , Alexander Gordeev , Andrea Righi , Ben Segall , Christian Borntraeger , Danilo Krummrich , Dietmar Eggemann , Greg Kroah-Hartman , Heiko Carstens , Johan Hovold , Jonathan Corbet , K Prateek Nayak , Mel Gorman , Mete Durlu , Randy Dunlap , Rasmus Villemoes , Shuah Khan , Steven Rostedt , Sven Schnelle , Valentin Schneider , Vasily Gorbik , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, driver-core@lists.linux.dev, linux-s390@vger.kernel.org, Yury Norov References: <20261101192203.6979-1-ynorov@nvidia.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: AW1haW4tMjYxMTEwMDAzNiBTYWx0ZWRfX5pCaNYyeS0GK /qoKN2A6JamDgryJ+BemvZnw4QGpf+1XjEjgUG26sziaCDm4OHmG0ASXzl4FJdoOB+vr8TLa+Dy dwoirZ0OEIYOZAC4O2tEq+j8pC7vmuA= X-Authority-Analysis: v=2.4 cv=HbCB3SE8 c=1 sm=1 tr=0 ts=6af2e0dc cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=Ikd4Dj_1AAAA:8 a=S2HyHEYmQh1kXY00aCwA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: V0Qpv5g5dMd40m2X4caVWzhKaZKP2Zbn X-Proofpoint-GUID: R0Mklm7znZwmumFMQXCwYU792AB9pLQO X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTEwMDAzNiBTYWx0ZWRfX0P2aS5Fa+IjE mHvDmDdBXSkhujTEso78l7iZZnVhWCSaLmH1Ds1/nVG3OGRd/1ItjrGH9YblNZ2usmsDUKhMbr6 ETpmBzrql1By6360fUq2AKCeiK1VWwur8GbZ2tgegDqcNKFpF7+LkUKjCmPNocXZ/p8G9YnS8Iq 8Z/uRmeVSEwiLM/eO+a1OVE6z+UcwoAq2jdrvL7iGuzuhkRu2n+s5lWdfzKhGSntm+4MwU0ZiOp Hlae7G3URIEak5gaQvA6CtZGdfWkfL+M4EfZE1I5yOf6d2bovikSW0xX21nN8b8x1qenDf4Etof slwHP2ByJHiTcptVrjFg4Fe9EcNld/VgjHkyITUpqZOUCHLLw7nRKMsZbhjTBQsH9XLKFuV6Npo 8Qtb2ldPGC2sazaM0hR+IYAEDisGI0WyokszlznYVpGj2sp43amYRM3Jw6cyxcTjXSGWKHhPWVU GxDfYJOEu23bI9c4IYw== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-10_03,2026-11-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 adultscore=0 spamscore=0 bulkscore=0 phishscore=0 impostorscore=0 priorityscore=1501 clxscore=1011 lowpriorityscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2611040001 definitions=main-2611100036 Hi, On 11/10/26 8:45 AM, Maxim Kuvyrkov wrote: >> On Nov 2, 2026, at 08:21, Yury Norov wrote: >> >> The preferred CPU mask currently lets the steal governor reduce vCPU >> demand when physical CPUs are contended. This series adds manual control, >> opening more use cases. >> >> For example, setting CPUs aside for selected fair tasks at runtime while >> steering other fair tasks toward the remaining CPUs. > > Hi Yury, > > I've been trying to do this with crutches in user-space for a long time. Thanks for implementing this in the kernel, and with a convenient user interface. > >> >> A user can mark a CPU non-preferred and pin a workload to it. Fair tasks >> whose affinity includes preferred CPUs are steered away, while tasks >> whose allowed CPUs contain no preferred CPU can still run there. The CPU >> stays online, task affinity is preserved, and the selection can be >> reversed without rebooting: >> >> # rmmod steal_governor >> # echo 0 > /sys/devices/system/cpu/cpu3/preferred >> # taskset -c 3 ./my_workload >> # echo 1 > /sys/devices/system/cpu/cpu3/preferred > > My use-case (being a compiler optimization engineer) is to pin benchmarks to specific cores, and stop the system from using those cores even when the cores are idle. This prevents L1/L2 cache pollution and makes performance numbers more stable. > Do you change it when running workload based on any signal/event? or you set it before starting it? If it is set before starting, you might as well offline the CPUs to achieve the same. I assume you are managing the preferred CPUs manually with write interface. You can do the same for online state. (Though it takes a longer) > Thanks! > > -- > Maxim Kuvyrkov > Garden City Compilers >