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Tue, 7 Jul 2026 07:16:57 +0000 (GMT) Message-ID: Date: Tue, 7 Jul 2026 12:46:56 +0530 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 21/23] virt/steal_monitor: Add direction control 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: <20260701141654.500125-1-sshegde@linux.ibm.com> <20260701141654.500125-22-sshegde@linux.ibm.com> From: Shrikanth Hegde Content-Language: en-US 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=KsJ9H2WN c=1 sm=1 tr=0 ts=6a4ca7f7 cx=c_pps a=bLidbwmWQ0KltjZqbj+ezA==:117 a=bLidbwmWQ0KltjZqbj+ezA==:17 a=IkcTkHD0fZMA:10 a=RAioF0-LDSMA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=iQ6ETzBq9ecOQQE5vZCe:22 a=VnNF1IyMAAAA:8 a=b52Ekj5tBG3iIJtAnKIA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYwNzA3MDA2NCBTYWx0ZWRfX8kqxFkxnVkWf 7L+F6eK536LwWd9kddeZGv7/lZzRNYsDCFItg42Zzrn9dReJvTHOZ257JddQhSbPnYzkgZt1p2Z acO67KagWvMkAfeK+DEs3LO0uxycL/k= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNzA3MDA2NCBTYWx0ZWRfX/b50KKCMtvn7 +6eLknsxYPDRlEcJcUirxKSdO1ya4RYLIqmKZ6PLkrbgS1rt7lXKzwdt2HuwkDr8pF8IaJRM8IB iUKs4PkK6SzsRyXm3/Jyh0f2hqLzEtQYo37sgGtmu6mqF36ykkcD3Kc45mf8DZBJnunnN4Ak0r7 q9QYGm4YaJlomsTdY75POPQudxJs86wihlnjMTrpNKrAAL+ZNaNZ+bjbwmHU/o3yPkikbdfx7iQ hMHCk9BWITLIYyl/YUvYsq95QaOWiTz7U6HIY8Q+AOizUTv9eQKikVpx9oU8sCXFSAIO0Dkvuhg vT3uSy8KMFA5bhcSu6ZsYgEfDEfos4vz/euw4BYocDDrjEEt0beXk/zWRmtsewwfIgARcXWj/7l Uu7aIJHUVP2nQ478nG9dI1CtHi1kX5iNRvOfVgWjHo8rc/opYAjN/08LR1xxeMtYB1eNHNcYXtA jcDGe3yyhbz9P9aKdIg== X-Proofpoint-ORIG-GUID: nHwfe_7z3UoVyYtp4ZSTjZEkwBZMDF29 X-Proofpoint-GUID: TN8EcUOkXOea8uQRdL7vFR4m4sOWAGHE 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=2026-07-07_01,2026-07-06_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 malwarescore=0 spamscore=0 adultscore=0 clxscore=1015 suspectscore=0 lowpriorityscore=0 priorityscore=1501 bulkscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2607070064 On 7/7/26 2:06 AM, Yury Norov wrote: > On Wed, Jul 01, 2026 at 07:46:52PM +0530, Shrikanth Hegde wrote: >> 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 */ > > Increasing the gap between hi and lo_threshold helps to avoid > ping-pongs. Sure. > >> + 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