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Wed, 1 Jul 2026 14:17:56 +0000 (GMT) From: Shrikanth Hegde To: linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net Cc: sshegde@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, 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 Subject: [PATCH v6 04/23] sysfs: Add preferred CPU file Date: Wed, 1 Jul 2026 19:46:35 +0530 Message-ID: <20260701141654.500125-5-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260701141654.500125-1-sshegde@linux.ibm.com> References: <20260701141654.500125-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: Skcjt2DKyiYSWtPamZKTLmtssWK8fJkK X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAxMDE1MCBTYWx0ZWRfX+XUOzsemHPKa lM/eTkeBEgJcC+V5Qnx1H1U6gSWh8QkJvVr7PJ+rQn6EnXKsbUbOYj6e/4sQqaltiWJkDtd9QZh +xi7d0d7++ztCYpTSFyVFOnnmkY7Ruo= X-Authority-Analysis: v=2.4 cv=edsNubEH c=1 sm=1 tr=0 ts=6a4521a8 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=md4hqiRJsRObfrzgdmAA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzAxMDE1MCBTYWx0ZWRfX1fM5puy2/pa4 Kux8z5iBGQ5T4HNH43aXPG+yP48hrcaCi5sUVrmHLIccT21AHJqfRzL8cb/Awr3LCihhImZa/T9 wD96xHdMle/AitaZmx6Uj9+GsXYyq8z/ZpPh/09dyho6NLirEnzQ13qfh+zQC/pnR2lfLw0X+W5 zYJREhKBXu+hT0tbNxT1nKsBQ+C6VL7r71x28peJfQZui/ifr6QR0m8/aMjdnl6wjbwa2cvrfTK tEoJEM4Tv88zhtmyo7UJgH96zphr8MZA+cqaMLbsngzLpH3SW/ne4mSNgbKwpkanouA512ukjrd OhOorX9k8VnJUvIaNxBDQMYv8RC/Z1zkXBsCHnTz/uxD24EvN8d6LfhsR37cWvM4k3gXzJxZhcc 1dxCU7poaVcQGw9WNVcMQZNxxO1qknp/ymEz7qTRsZKuKKYzNx88c4aF4/7YnDJaFYGYUCUL8Vy 0Z8vn9i9nZa57rjAF5A== X-Proofpoint-ORIG-GUID: EptDlQYxw9wzaU7JRV4aHIAPPOw16fWf 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=2026-07-01_03,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 adultscore=0 impostorscore=0 bulkscore=0 spamscore=0 suspectscore=0 clxscore=1015 lowpriorityscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607010150 Add "preferred" file in /sys/devices/system/cpu This offers - User can quickly check which CPUs are marked as preferred at this moment. - Userspace algorithms irqbalance could use this mask to send irq into preferred CPUs. For example: cat /sys/devices/system/cpu/online 0-719 cat /sys/devices/system/cpu/preferred 0-599 <<< Implies 0-599 are preferred for workloads and 600-719 should be avoided at this moment. cat /sys/devices/system/cpu/preferred 0-719 <<< All CPUs are usable. There is no preferrence. Signed-off-by: Shrikanth Hegde --- Documentation/ABI/testing/sysfs-devices-system-cpu | 11 +++++++++++ drivers/base/cpu.c | 8 ++++++++ 2 files changed, 19 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 82d10d556cc8..ac1dbb209cc7 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -806,3 +806,14 @@ Date: Nov 2022 Contact: Linux kernel mailing list Description: (RO) the list of CPUs that can be brought online. + +What: /sys/devices/system/cpu/preferred +Date: July 2026 +Contact: Linux kernel mailing list +Description: + (RO) the list of preferred CPUs at this moment. + These are the only CPUs meant to be used at the moment. + Using CPU outside of the list could lead to more + contention of underlying physical CPU resource. Dynamically + changes based on steal time. With CONFIG_PREFERRED_CPU=n it + is same as active CPUs. See sched-arch.rst for more details. diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 19d288a3c80c..4ac990efee7c 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -391,6 +391,13 @@ static int cpu_uevent(const struct device *dev, struct kobj_uevent_env *env) } #endif +static ssize_t preferred_show(struct device *dev, + struct device_attribute *attr, char *buf) +{ + return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_preferred_mask)); +} +static DEVICE_ATTR_RO(preferred); + const struct bus_type cpu_subsys = { .name = "cpu", .dev_name = "cpu", @@ -532,6 +539,7 @@ static struct attribute *cpu_root_attrs[] = { #ifdef CONFIG_GENERIC_CPU_AUTOPROBE &dev_attr_modalias.attr, #endif + &dev_attr_preferred.attr, NULL }; -- 2.47.3