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Fri, 24 Jul 2026 14:08:33 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.20.178]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 24 Jul 2026 14:08:32 +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, jgross@suse.com, virtualization@lists.linux.dev Subject: [PATCH v9 03/11] sysfs: Add preferred CPU file Date: Fri, 24 Jul 2026 19:37:24 +0530 Message-ID: <20260724140732.2683314-4-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260724140732.2683314-1-sshegde@linux.ibm.com> References: <20260724140732.2683314-1-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-Authority-Analysis: v=2.4 cv=HJXz0Itv c=1 sm=1 tr=0 ts=6a6371ee cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=Tj8IOOKMsRt27BSU_nUA:9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzI0MDEyNCBTYWx0ZWRfX/Hssb720al8b OemehvFFUjZU5Oee/28d8A2qRpfKHh42MsZ6FpBNpRBqGqaEQdMKvAEXdktzXK5mcT6CZjp3MgN NCAuywNHIJNlfFXd4pp8qR0e1jO/ubTS/xfdLJLtWWNJ35MW5VfKCcva62kjmEg75O4AMO3WC8Y oVl1HtRpfecUj/Qme6jwLQ9MNbHPTwKMxXsDnA3yeyvG9nRzOZTRB4fYQSjdHEhQNawu7e6Qywb L5g6Zx+Jpb8xP97oXRxuWkU7zRT+9nxacFlvO+ElP7zXnYFuROqbcqo8YUkxqjFOOaeTDXQKU6G S9qkJV7wHmD0MsW6teWK3Xk+CeYTeP4g6CgedBEDdbglBojP2/jFiXdTanzMlXyzE2FrNd0PkYq JNk/qn4O34CQ1OUTKTKnzhKDXmRh7dX4+fdOAN0lf5xha0bbOu9uMrg+xmNRqlEYZtLfoHExguW p6t+50SPSoKDd30LuFw== X-Proofpoint-ORIG-GUID: cgBAhnZQYFIoBVBGjB4vV7_c1y7YgfTH X-Proofpoint-Spam-Info: AW1haW4tMjYwNzI0MDEyNCBTYWx0ZWRfX94ngc9Hf768e pHU12CgEy/k/hUIYr7mTsJZi5EQAfB2DwGzHUKWkw/8fOQHABIQ3swJI4+oOa0OsXBr6F4qV9Gl 6SfAiadGqYxjt0pl8VQ6XaUaU3uNUpE= X-Proofpoint-GUID: yFy6dgR4DU7Y35uG7-ys7y_btMvsbmQX 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=2026-07-24_03,2026-07-24_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 suspectscore=0 malwarescore=0 impostorscore=0 clxscore=1015 phishscore=0 spamscore=0 adultscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607240124 Add "preferred" file in /sys/devices/system/cpu This would help - Users to quickly check which CPUs are marked as preferred. - Userspace daemons such as irqbalance to 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 | 14 ++++++++++++++ drivers/base/cpu.c | 12 ++++++++++++ 2 files changed, 26 insertions(+) diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu index 82d10d556cc8..676412c46b2a 100644 --- a/Documentation/ABI/testing/sysfs-devices-system-cpu +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu @@ -806,3 +806,17 @@ 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 applicable in + paravirtualized environments. + + The steal governor driver dynamically adjusts this mask + based on observed steal time. Scheduling tasks on + CPUs outside of this list may lead to performance + degradations due to underlying physical CPU contention. + + See Documentation/scheduler/sched-arch.rst for more details. diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 19d288a3c80c..5da2a96fb37e 100644 --- a/drivers/base/cpu.c +++ b/drivers/base/cpu.c @@ -391,6 +391,15 @@ static int cpu_uevent(const struct device *dev, struct kobj_uevent_env *env) } #endif +#ifdef CONFIG_PREFERRED_CPU +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); +#endif + const struct bus_type cpu_subsys = { .name = "cpu", .dev_name = "cpu", @@ -531,6 +540,9 @@ static struct attribute *cpu_root_attrs[] = { #endif #ifdef CONFIG_GENERIC_CPU_AUTOPROBE &dev_attr_modalias.attr, +#endif +#ifdef CONFIG_PREFERRED_CPU + &dev_attr_preferred.attr, #endif NULL }; -- 2.47.3