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Thu, 9 Jul 2026 21:57:15 +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 v7 03/12] sysfs: Add preferred CPU file Date: Fri, 10 Jul 2026 03:26:39 +0530 Message-ID: <20260709215648.1246821-4-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260709215648.1246821-1-sshegde@linux.ibm.com> References: <20260709215648.1246821-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: linux-kernel@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-Authority-Analysis: v=2.4 cv=Q/XiJY2a c=1 sm=1 tr=0 ts=6a501949 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=md4hqiRJsRObfrzgdmAA:9 X-Proofpoint-GUID: Bw-7cGqKhZrIEmfXAfabpSZ1wmvL58ER X-Proofpoint-ORIG-GUID: JoeWxLCuNdg5-T0iONB7MkOPRNfJVAn7 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA5MDIxOCBTYWx0ZWRfX8blbPTVeYmqt 9owElbmhLSuT6WCIJ0L4ChurMMu87Emmw3MSTUJ6RRbdUPZv7mI9xCz0oAZe4cKI7Ku1TXl8mQb t3IAn0y6udpmU/FlsunlcE26OZlOdtE= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA5MDIxOCBTYWx0ZWRfX/2Qla959E8sZ G0KyROHeRXB/VQYFNTMaY8ppygHYGy7u/luSm4DfLYccqWuBZ/CjXFnTBCfXQdnTBpjTM5bWMW0 RMkXGLbDow8Ab7MXjyjwlVmYklmn1pf5o+P6D8Oeb8oSjPIatEhsOovAkzUMq9OUZy+On7vuyqc rs7la/09FLMTYyZ1FiDJp4h0448ZVHUkjUZXZCenM1hQyS9lmv2K4MOaoYnWY0I7IkCIORY+/Fn Oyg8FSAhYnnvhaZuf/0zMMBS3VrXjIaelUwnuQxP+qwtr1P/xu18jN0M+SVGvmxM7zeL8+mKxq1 9q/kqZ7eNru+6Jq9Pr8tsquVT3cq2XgKrL4vyuN37c0CuEGic2p9tl+0nPDdkpzNHkcOSfXTMBM XIGJ5Hb3r39yiZSHZcIq7QHInbCyZ5VHUaZQuHrgE7h/ZTJwxCQk9e9TbzEC1MFfoZ+98heLty4 EQiS8NzauVJAsqftBaA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-07-09_04,2026-07-09_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 adultscore=0 impostorscore=0 spamscore=0 phishscore=0 priorityscore=1501 bulkscore=0 clxscore=1015 lowpriorityscore=0 suspectscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607090218 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 preference. 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