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Thu, 3 Sep 2026 06:33:30 +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, meted@linux.ibm.com, ynorov@nvidia.com 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, sunlightlinux@gmail.com Subject: [PATCH v12 05/13] sysfs: Add preferred CPU file Date: Thu, 3 Sep 2026 12:02:32 +0530 Message-ID: <20260903063240.268775-6-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260903063240.268775-1-sshegde@linux.ibm.com> References: <20260903063240.268775-1-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-Spam-Details-Enc: AW1haW4tMjYwOTAzMDA1NyBTYWx0ZWRfX5kLtQsPMI8yn cMuuODvQwhL9RsAXQLQc1zOkjIwVsokJ66GEaM+8iaSmfIdXmAVzRxP+0f1ROSzmFAVkgwFTt9Q 03/DLEVcxu3xWI9RXU/EgZ2qAsx7zH1oA22pnIKxrVFdeao7E8B1kzilTY/RtLPo6X6616M5UYF kSNf/7yJpHAODnj/Nm6TUnJ2VyEzeUfGQM2Qss668kjnr27n00A1XRJA58x9h5E/r22KoPTB1mB E9VAu2KOWLfv3UNDxm7vx8GnNBpRsfPkdEOIsNYVHuZqnpp9XwLUC5P5wW2XhMXJsx/xM15/ejT i3HY7Q/WCcjp9mxSabWLzEKF8czArofFDePXTJWFgA0iAQKwNTDAxBeSS+brejNn9g1GBIixNxx vBx6413nqnrW9Gd3TKmqAZ3MRFDuK17j0kWBHy5fVPqgFkH8TDn1hxLlow1UFzF1T6IbBOfuvf3 Ukr6jgdjl0bGAdsBZRQ== X-Proofpoint-ORIG-GUID: nzvIYDW2euOOE5HIZDo3qhnC_PGk_VRs X-Authority-Analysis: v=2.4 cv=CNgamxrD c=1 sm=1 tr=0 ts=6a9914c8 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=94fVmjRkuoLjN79_KVgA:9 X-Proofpoint-GUID: qKhVofSj-YCpys3f_KC3-a1DgfgihM7N X-Proofpoint-Spam-Info: AW1haW4tMjYwOTAzMDA1NyBTYWx0ZWRfX7WxTtjI3ksIs BJNC5Fo91kO9B+raIrWGZwW36+7fyQ2ihRzdXFEwNsWL5pJA+n9VOc8o3tFrlJs3W3XvGfuEwsv wRzxF/LkVEh7X/UOGdfPOGfdVd8bJrA= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-09-03_02,2026-09-02_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 bulkscore=0 suspectscore=0 phishscore=0 lowpriorityscore=0 priorityscore=1501 clxscore=1015 impostorscore=0 adultscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2609030057 Add a "preferred" file in /sys/devices/system/cpu/ when kernel is built with CONFIG_PREFERRED_CPU=y. This would help - Users to quickly check which CPUs are marked as preferred. - Userspace daemons such as irqbalance to use this mask to route irqs 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..8f250b8693b8 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: Sep 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-paravirt.rst for more details. diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c index 69e52fed4241..747915ff974f 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 }; -- 2.52.0