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Wed, 1 Jul 2026 14:21:56 +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 21/23] virt/steal_monitor: Add direction control Date: Wed, 1 Jul 2026 19:46:52 +0530 Message-ID: <20260701141654.500125-22-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-Authority-Analysis: v=2.4 cv=a4kAM0SF c=1 sm=1 tr=0 ts=6a452297 cx=c_pps a=aDMHemPKRhS1OARIsFnwRA==:117 a=aDMHemPKRhS1OARIsFnwRA==:17 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VnNF1IyMAAAA:8 a=_v5trmpiMvKuf-VRmTkA:9 X-Proofpoint-ORIG-GUID: v023rTD_snh8wzQFuuprIZgRx5V0sDuX X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzAxMDE1MCBTYWx0ZWRfX25Osvz64kISd isK8aKtX/7lhNX1u/jBVAEOGPeXFF6f8OklmoE76XzI7QJBxt4gIMsghI2AeVCWE8umGehWB+KO wrZUdLVIQPGFBdnJ7ZGFoXUJ+WIkhD1AuwSaprqM/YQRnhoBbevpKbcRsaxZCOiHHRNXCc9CaqW hKlGgBuLRp1IPTm3jlxjdLGS++XjjzCyGEKw7OoGXaV7p1DPR9o5eSSdiun/kljobRzON95XR9O 5/yJVmA5LS51dCPMBhzFMOHpisq5v/zN+8+GDWAOeTi/FUI2q/AbWmCEtgfB/O6/3IdfbpQ4B+1 SHtpyjbJoA1ied6l2eifVNUSmHJNxh4lk296HfpivY3RVnsfsAcUl8maeEfNBdI3F2/n/SvYmFL A57rxzq2A6lmP7OJ+vrc32VvannLM7RWJg/bfp+xMD8JfD0HkqQDEJYVRSTRPDAuBUjDrkFtTYR NUnj2OSR3u49QNLugcQ== X-Proofpoint-GUID: 1NO0sV_M21SWjFDo9JgXd-JxcfrK_-R8 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzAxMDE1MCBTYWx0ZWRfXzGxs+6DTEpRx 2pIYeUDdGWSFrqFMInyN6Pk0JbMw/o+CoTc15+MQOWXcw3CiYFGxIQoOsBzkmj5d+mIZX3Dn9nz DXxLzw/mguQcoXgyxT1vNr6PmdxdsfA= 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 clxscore=1015 bulkscore=0 suspectscore=0 lowpriorityscore=0 impostorscore=0 spamscore=0 priorityscore=1501 adultscore=0 malwarescore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607010150 Cache the previous direction on steal time. So two consecutive values of high values or low values are taken for decrease/increase of preferred CPUs. This helps to avoid oscillations. Signed-off-by: Shrikanth Hegde --- drivers/virt/steal_monitor/sm_core.c | 20 ++++++++++++++++++-- 1 file changed, 18 insertions(+), 2 deletions(-) diff --git a/drivers/virt/steal_monitor/sm_core.c b/drivers/virt/steal_monitor/sm_core.c index 7b7435f79b85..4810bad96818 100644 --- a/drivers/virt/steal_monitor/sm_core.c +++ b/drivers/virt/steal_monitor/sm_core.c @@ -20,6 +20,12 @@ struct steal_monitor sm_core_ctx = { .low_threshold = 200, /* 2% */ }; +enum sm_direction { + SM_DIR_INCREASE = -1, + SM_DIR_NONE = 0, + SM_DIR_DECREASE = 1, +}; + module_param_named(interval_ms, sm_core_ctx.interval_ms, uint, 0644); MODULE_PARM_DESC(interval_ms, "Sampling frequency for steal values in milliseconds (default: 1000)"); @@ -59,12 +65,22 @@ static void compute_preferred_cpus_work(struct work_struct *work) steal_ratio = div64_u64(delta_steal, delta_ns); /* If the steal time values are high, reduce preferred CPUs */ - if (steal_ratio > sm_core_ctx.high_threshold) + if (sm_core_ctx.prev_direction == SM_DIR_DECREASE && + steal_ratio > sm_core_ctx.high_threshold) decrease_preferred_cpus(&sm_core_ctx); /* If the steal time values are low, increase preferred CPUs */ - if (steal_ratio <= sm_core_ctx.low_threshold) + if (sm_core_ctx.prev_direction == SM_DIR_INCREASE && + steal_ratio <= sm_core_ctx.low_threshold) increase_preferred_cpus(&sm_core_ctx); + /* mark the direction. This helps to avoid ping-pongs */ + if (steal_ratio > sm_core_ctx.high_threshold) + sm_core_ctx.prev_direction = SM_DIR_DECREASE; + else if (steal_ratio <= sm_core_ctx.low_threshold) + sm_core_ctx.prev_direction = SM_DIR_INCREASE; + else + sm_core_ctx.prev_direction = SM_DIR_NONE; + /* At least one core is kept as preferred */ WARN_ON(cpumask_empty(cpu_preferred_mask)); -- 2.47.3