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Tue, 25 Aug 2026 10:39:58 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.21.103]) by smtpav07.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 25 Aug 2026 10:39:58 +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 v11 04/12] sysfs: Add preferred CPU file Date: Tue, 25 Aug 2026 16:08:47 +0530 Message-ID: <20260825103855.721013-5-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260825103855.721013-1-sshegde@linux.ibm.com> References: <20260825103855.721013-1-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-Proofpoint-Spam-Info: AW1haW4tMjYwODI1MDA4OSBTYWx0ZWRfX5cvotuUGpPDY bW5JSdonH54o3AsAqyECUDBUaPSkl7Fp8tQ07rGM4DX9eIX4uWPtXMXLVGO6q36s4xuwKRqwbPQ dVML3+XcCj+xUqgNUhjPq1QQkRSZK+M= X-Authority-Analysis: v=2.4 cv=AYuB2XXG c=1 sm=1 tr=0 ts=6a8d710d cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=94fVmjRkuoLjN79_KVgA:9 X-Proofpoint-ORIG-GUID: nKLWTKMyAO9f1eo0MzZ6vfuY9c7p0f_l X-Proofpoint-GUID: VYSb_-2GSExxITTP6TGFadWd3vhICmiT X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODI1MDA4OSBTYWx0ZWRfXwN+/DWK8Lvmj za/RYqL0PdoVSlbfND3FSPceAWY/vCaGd1fMB/QrfRjbH4zbUSiKQuatVw1rFXtPEKSSxgMPXbt WZv5HSETWMFakQGWUQ0GEVeAHz6U9tk9jdBnF4pDROAzcJRiKiC5zH0fI/GfOtI0XB7Egtmkqwk NkLM9Mac17BN82urmV6DgNMvFpMlRHTib8UJGTiN1oB6tbC7iLT3sIOVuPFdYm4kT4OYOurPgWk SJ2NTGRJsLFHLClmfW79MmTA256w5Ufe+F3kZQGDlDHtT92PdVlqmHIf+zhdi4czvZiKH3RFqlp epm0YgK0ck+FHXdxv4mfbvkZrN2mIybtjppq/D35npICsTrgHrsdXaMLCKvF8uAEL2WcYsK2KfZ fh2Jme5ICzy8XIbw8vUCjQdBQ+XOEcBFsbV9oqcj0H36xa/Mw+EIOuBQZqgBd0x8Z6GyT5fkKXj 1CXZMnSDhwPjOrGkn5g== 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=2026-08-25_02,2026-08-24_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 phishscore=0 clxscore=1015 adultscore=0 bulkscore=0 impostorscore=0 priorityscore=1501 lowpriorityscore=0 spamscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608250089 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..080c69aca4f0 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: Aug 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 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