From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 31399566C66 for ; Wed, 9 Sep 2026 13:57:48 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.163.158.5 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788962269; cv=none; b=HMgS11RGWBGf0o8MktlTl7IoQFCBdkYFt3p08LEO0LfGvefssg3G6NHqS2DvI3VzLaLekc+AzVQ5vFaSL0RRjty0m2VA0Iym0b+z4AQLefgGDfPgwu5BRU5wBRelUf8uWH1yKbO0W1gm5Pwrj3pSgE9WgnEq7r5d1T8fy+2wls0= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788962269; c=relaxed/simple; bh=KRcnPZxJ3TxjYbvZ/ffwiydMHYyd7oDraGjHWCGvvcs=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=JDhhAZEZUSlniqKIUZDv7kg97Cns4Wf2EYpFqMDwGKXHnYcmETOFH/5dl93enftueLVbz+8HJZZ4S/jDbZmW5m/rAvbXh3BuRWmj53ptyiOMNkbKUgnsJGH3Sm8izAlk0i52/hKZo8nT8/iKQinE1XieY/8wKNjf7jjNjLMAY50= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b=pvnbzR0y; arc=none smtp.client-ip=148.163.158.5 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ibm.com header.i=@ibm.com header.b="pvnbzR0y" Received: from pps.filterd (m0356516.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 689B1ktF3669941; Wed, 9 Sep 2026 13:57:35 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:date:from:in-reply-to:message-id :mime-version:references:subject:to; s=pp1; bh=zmk93sQzf03EanZhV Bee2OYiiS4IEVygsO5Vm1CSPyc=; b=pvnbzR0ylmPna7lHdHrMuFADljixaIfSW yx64r50kn51SEGl1AtMTkJKCmJn5+dkhJL+Q5QVvMEWU0+tTzo+To71gLB+rwYX5 AxJJ/rxp7+0vB8IH2j7mNctRexFkiVAkzlcd6E0IwIjQl4de+Ad3D7O3rNjfbXY9 J4fvhV5wE/W5QZYRR3aX0W2M69IU8ZackNl7OpY1NwRvki3+qm8fNGH1s+CuIoaJ wrQcFftGGhvjGwdbpd6Om9aOJW4F2TlbE/AjdIBkeuNU0jzQ3OkTbrof3yiF3tQw u7Q0RuNURQFlcdLb04tNj3r2Z3E1eulIw1LgBwfp+vPr97FHR/IwQ== Received: from ppma22.wdc07v.mail.ibm.com (5c.69.3da9.ip4.static.sl-reverse.com [169.61.105.92]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4ggbj8dvjd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Sep 2026 13:57:34 +0000 (GMT) Received: from pps.filterd (ppma22.wdc07v.mail.ibm.com [127.0.0.1]) by ppma22.wdc07v.mail.ibm.com (8.18.1.7/8.18.1.7) with ESMTP id 689DuDJU008335; Wed, 9 Sep 2026 13:57:34 GMT Received: from smtprelay02.fra02v.mail.ibm.com ([9.218.2.226]) by ppma22.wdc07v.mail.ibm.com (PPS) with ESMTPS id 4ggwswapwd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Wed, 09 Sep 2026 13:57:33 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay02.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 689DvSiI52101410 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Wed, 9 Sep 2026 13:57:28 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id DB16720043; Wed, 9 Sep 2026 13:57:27 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id EBD9220040; Wed, 9 Sep 2026 13:57:16 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.124.210.73]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 9 Sep 2026 13:57:16 +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 v13 05/13] sysfs: Add preferred CPU file Date: Wed, 9 Sep 2026 19:26:09 +0530 Message-ID: <20260909135617.871006-6-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260909135617.871006-1-sshegde@linux.ibm.com> References: <20260909135617.871006-1-sshegde@linux.ibm.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev 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: 621YhHMb7To8WUIq3rA2CXvj0gKxvm4Q X-Proofpoint-ORIG-GUID: iUrGee2DfGJb7H_zlzgj3bZ9OkrRLBXW X-Authority-Analysis: v=2.4 cv=RNCD2Yi+ c=1 sm=1 tr=0 ts=6aa165cf cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=VdqzKS8jKosA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=94fVmjRkuoLjN79_KVgA:9 X-Proofpoint-Spam-Info: AW1haW4tMjYwOTA5MDE1MSBTYWx0ZWRfX4fb9WAYx0lrg KfhLavjxAczgpKyXFSqhpYVN+9XpWDdg7/kYQvhNKATqcROE6n767aJ3mt0v8VSfEo1rfRikkbt RNiXtTI3Yq7va2sUwJRV1jNtM5c8Sv4= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwOTA5MDE1MSBTYWx0ZWRfXy7ckDJUon3md f5fMxWzYkeLp1z81yXrT38+vMIUCtv6SluaG5/Moe30Z54MZl1cgYx5gzI6x49Zq04cbf9ewSkT 5QX8/mnm5c0H8kNob9WOgz1lnfOzDa6fbaRzJzchy8zKPpHhDaVHOWiddfeJGZOITjyyvw3dIHF f2E6NlyzVnkGCiANMOjhLx0X35nXlFrmPGhwd2dFNf5eW1UllkJLs8V6ftPNsc4bxnFkbTP6xYa nSAywXqF9S6j3buvw+YrZAqhexLy/2J2YhsCx2RDxFXHATUgsgElHi/m5VdwqrlWpp/N18Qf/w7 O+Rn/WSh8z3FcOGtBQJFoxnwKzQgzqjDyEZPsxsu7S0tyNkF8y5ud895zCZe49fvKG9b0DzWD4S HNLNNHhKUc/tgmVQPErcB6S6UrOyk4fBbsMyLiuwNmOuRguOvsQxfrbfCZYjtBpwSbZNzcLdvHH iL5Uc4nD1talgN64cmA== 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=2026-09-08_03,2026-09-09_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 lowpriorityscore=0 bulkscore=0 clxscore=1015 spamscore=0 impostorscore=0 adultscore=0 phishscore=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-2609090151 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