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Fri, 10 Jul 2026 17:00:44 +0000 (GMT) Received: from [9.124.216.30] (unknown [9.124.216.30]) by smtpav02.fra02v.mail.ibm.com (Postfix) with ESMTP; Fri, 10 Jul 2026 17:00:44 +0000 (GMT) Message-ID: Date: Fri, 10 Jul 2026 22:30:43 +0530 Precedence: bulk X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 03/12] sysfs: Add preferred CPU file To: Yury Norov Cc: 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, 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 References: <20260709215648.1246821-1-sshegde@linux.ibm.com> <20260709215648.1246821-4-sshegde@linux.ibm.com> Content-Language: en-US From: Shrikanth Hegde In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=M7J97Sws c=1 sm=1 tr=0 ts=6a51254a cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=VwQbUJbxAAAA:8 a=f7GhLAGFv2NyNaRqmGgA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzEwMDE2OCBTYWx0ZWRfX0ue827LpTDR3 UPkGZsXDXzhdp8ZxmaEH+0GI9Hplj9e2BQEiVEs/9g0BlnmlQPXiFawAk1ftiL6Bk736C9WZof3 nt8/GYM2UFf03LoeGo1ntsokHpJzHkOgWAeRMxw6oMzciv4zLQSjfPbXSP9IiZyAgVNBDodT1nn IxvTtdpKLgz+xqjiu8dwCyFB0Cg4mPVuSSvg+oYkmYlcwYTd+TZ6sNJFmUH4Ta085DQyPK9fnTI 7VFq9oLRtrNCt/CWKXXWHDnrrZOJ1LJfIzaxnZOdoaAAztPXcsJJWdcI9d+5fNtmivRrU1IFHIL DnQomteW8m5x5uXQ+jXidgeb8RIuNAhSCCvAP7gqYjhPS6NvDAoH0xwv9ogZXox23MHt/Ow7ui2 YZ9I12WcxENQT1gVbobOqXhgF9ZiNZrBGf9g/pD2pv5WAFvqYCZnc9pq7ZB9UNqV7XU8bVYqZOp IkgEDB05VGxhLYUP83g== X-Proofpoint-Spam-Info: AW1haW4tMjYwNzEwMDE2OCBTYWx0ZWRfX3keYd35B3D0U n39roeHIm7vV5kY7d7XwpiefBxLDybb+jYChSr+42D2qe17nbGHbI/+n3T2fplmMpMPPvtxKnLe olqCs7AiOdonNXJV0EugLc7qcqofdJw= X-Proofpoint-GUID: t0Po62chkBLVtpus0_5t3WT5pDCwiBg7 X-Proofpoint-ORIG-GUID: -5m9RnASPag7_uJm3zgRH7mwp0d0iiEE 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=2026-07-10_04,2026-07-10_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 lowpriorityscore=0 malwarescore=0 clxscore=1015 adultscore=0 priorityscore=1501 bulkscore=0 spamscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607100168 Hi Yury, thanks for taking a look. On 7/10/26 9:11 PM, Yury Norov wrote: > On Fri, Jul 10, 2026 at 03:26:39AM +0530, Shrikanth Hegde wrote: >> 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. > > This should mention that it's about paravirtualization. Ok. I will rephrase it. > >> 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, > > #ifdef CONFIG_PREFERRED_CPUS ? Not needed no? It will print active CPUs. > >> NULL >> }; >> >> -- >> 2.47.3