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Wed, 1 Jul 2026 14:17:28 +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 Subject: [PATCH v6 02/23] kconfig: Provide PREFERRED_CPU option Date: Wed, 1 Jul 2026 19:46:33 +0530 Message-ID: <20260701141654.500125-3-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260701141654.500125-1-sshegde@linux.ibm.com> References: <20260701141654.500125-1-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: AW1haW4tMjYwNzAxMDE0NSBTYWx0ZWRfX5NJez2By3EHv kxMPr3HnI56LsmHeAHbj4Kqbi6li/aZwQbB5QgAKQxtU7qa7XKyvcUKgoIX5J9JEB8+CZi/LORl McsNVfDOGhLgIvG0sJff5E9ElsGu1ZY6zJrfOLB6pewQx8QD3dKxa9rhpagHDMO32uaUWnQQigT ur9sOn+E84V2wD0iT+gASP3/tR3QA/zLhFWVjEpySNJ4DYm1r/9o4d3HziZsk8oj7MUAI0nRvFc 92c9rBBAt0taa04B3wfhIrGSN60/yt/5XAy4c7qb5FgHzwiurUnTkiWh6m8/L9+EJOeTgzCCDoX 9/PTte7pKzWmf/XeGjNN3ZK1fe2B1ROX8R3kp1vNjQjoi29ue7fR2KgnZ90M+SaMT5X+nHhV4Af eHSVJgCptTNv/y8AkY04x2tuc9p+xs88yzTR2iOST3aEkG+8gMXrk+2TFJeIeiLSwwW6WZgM0oy fEOpB96qTTS+4T2x+uw== X-Authority-Analysis: v=2.4 cv=V45NF+ni c=1 sm=1 tr=0 ts=6a45218a cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=NEAV23lmAAAA:8 a=VnNF1IyMAAAA:8 a=BWPB87uJ6lDr-Q8--dwA:9 X-Proofpoint-ORIG-GUID: Q_hGE8EZ-uKJieGhFEryFqwX4ozMKPJX X-Proofpoint-GUID: a1pf1RueYaGyWzogejjjMDeypZzV4OtJ X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAxMDE0NSBTYWx0ZWRfX7cAECclg/9zh 68Wb7U5b+Zdr84vwzH11gbC68vnqtpz+dVKaPxlkK5WCItdaCT/ozN1c/KyKVeh6m1i2KSAfr5I CP6QQQIbtMKRF2wV186QfYVrr61nAfw= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-07-01_03,2026-06-26_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 suspectscore=0 lowpriorityscore=0 priorityscore=1501 adultscore=0 clxscore=1015 impostorscore=0 malwarescore=0 bulkscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607010145 Introduce a new config named PREFERRED_CPU. This helps to: - Avoid the code bloat when PREFERRED_CPU=n. In that cases preferred is same as active. - Avoid the ifdeffery around PREFERRED_CPU in many files. Since paravirtualized use case is the main driving force of this feature, make it default for kernels with PARAVIRT=y Signed-off-by: Shrikanth Hegde --- kernel/Kconfig.preempt | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 88c594c6d7fc..b3a543cb44cd 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -192,3 +192,17 @@ config SCHED_CLASS_EXT For more information: Documentation/scheduler/sched-ext.rst https://github.com/sched-ext/scx + +config PREFERRED_CPU + bool "Dynamic vCPU management based on steal time" + depends on PARAVIRT && SMP + default y + help + This feature helps to reduce the steal time in paravirtualised + environment, there by reducing vCPU preemption. Reducing vCPU + preemption provides improved lock holder preemption and reduces + cost of vCPU preemption in the host. + + By default preferred CPUs will be same as active CPUs. Depending + on the steal time when steal_monitor driver is enabled, + preferred CPUs could become subset of active CPUs. -- 2.47.3