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Wed, 17 Jun 2026 17:42:45 +0000 (GMT) Received: from li-7bb28a4c-2dab-11b2-a85c-887b5c60d769.ibm.com.com (unknown [9.39.28.77]) by smtpav06.fra02v.mail.ibm.com (Postfix) with ESMTP; Wed, 17 Jun 2026 17:42:44 +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 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, mgorman@suse.de, bsegall@google.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 Subject: [PATCH v4 03/20] kconfig: Provide PREFERRED_CPU option Date: Wed, 17 Jun 2026 23:11:22 +0530 Message-ID: <20260617174139.155540-4-sshegde@linux.ibm.com> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260617174139.155540-1-sshegde@linux.ibm.com> References: <20260617174139.155540-1-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: AW1haW4tMjYwNjE3MDE2NiBTYWx0ZWRfX603m97pKEm73 7tPJsiu9vDh3+txjpdA1/In4cLrv9SvP3iu/WjfzKtVNQokcT3isL0Buct5OMlkuwMQ770eSQKT /C5juYu/wHTnFNOd587YNnJ/+MUH1vY= X-Proofpoint-GUID: 8Ct6fqIrHtHzUBW8NKqcjuXEAhZbGdJr X-Authority-Analysis: v=2.4 cv=bMgm5v+Z c=1 sm=1 tr=0 ts=6a32dca2 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=FelO9ux0wxsA: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: HVR4pRsSXiy2fYDHb48RGImIo1QbyisC X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNjE3MDE2NiBTYWx0ZWRfX3/TvjPwhbdoz UlI2mXn9Qqaw4ita6RwVHCDRrz5DHmSaK9aNYfl+9CPVTGohO4MYvo1Erq+KYlSLjeHe2O5INB+ G4KAMrYsk2LhDbLdgykXJJjqKeQsx43FtmbvB7nZwtichNwbPI6I3ByJvBZN4z/DxMiLxtjspJc K+8MIKq+V/G0gmdOwwAcbwXdpiVIJy4sykGnuPvz3iao1fBXaS15MdwWPdfWSLepxZcrPk2ff2b XYhzHym/dWvlV2KObd4SVybnfslpxpP3xfOGb4HKHbc52Xfs9oa+4Tijam18pYdHfXqhnvc2yvc GJgkuFJktf+ujkGLnYvdfmTqIua5M4y4mSqA5ppAwEa+9LzkWVOiZ1jBV6SLrzYF/smOcxo3Wkr PbkzlVT5D0128R1kosyv0FlnhlAJtVR6yuA4nLeQ4+T9xnKv/kTXY8PAkUewh6YBJ0AI+mHRYyu v5AAofRHrSGjkd5gBHQ== 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=2026-06-17_02,2026-06-17_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 impostorscore=0 malwarescore=0 adultscore=0 spamscore=0 bulkscore=0 priorityscore=1501 phishscore=0 clxscore=1015 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2606170166 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 paravirtulized 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 | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt index 88c594c6d7fc..0995f5ba66eb 100644 --- a/kernel/Kconfig.preempt +++ b/kernel/Kconfig.preempt @@ -192,3 +192,16 @@ 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" + default y if PARAVIRT && SMP + 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 is enabled, preferred CPUs + could become subset of active CPUs. -- 2.47.3