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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 17 Jun 2025 16:00:11.2629 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 2fece2a3-0ccc-454f-8eb7-08ddadb80a37 X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: AMS1EPF00000043.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: GV2PR08MB9328 Hello Shaobo, On 6/16/25 09:14, =E9=BB=84=E5=B0=91=E6=B3=A2 wrote: > From: huangshaobo2075@phytium.com.cn > To: linux-pm@vger.kernel.org > Cc: rafael@kernel.org, lenb@kernel.org, deepthi@linux.vnet.ibm.com, khilm= an@kernel.org > Subject: [cpuidle] Limitation: cannot model asymmetric C-state latencies = on big.LITTLE SoCs > > Hi, > > I'm working on an ARM64 platform with a big.LITTLE CPU topology. While pa= rsing the ACPI tables, > I noticed that the C-state latency and residency values differ between th= e big and LITTLE cores, > as expected. > > However, I found that the current cpuidle framework only allows a single = global `cpuidle_driver`, > and all CPUs share the same `cpuidle_driver->states[]` array. As a result= , only the first core to > initialize (usually a LITTLE core) sets up the C-states, and the same val= ues are applied to all cores, > including the big ones. This leads to incorrect idle behavior on asymmetr= ic platforms. > > I believe this behavior was introduced by commit 46bcfad7a819 > ("cpuidle: Single/Global registration of idle states"). > > I understand this design was introduced in 2011 to simplify cpuidle and r= educe memory usage: > https://lkml.org/lkml/2011/4/25/83 > > However, on today's heterogeneous SoCs, this global model no longer suffi= ces. For proper modeling, > we need support for per-cluster or per-core cpuidle drivers, or at least = some mechanism to allow > different idle state parameters per CPU. > > Has there been any discussion or work toward lifting this limitation? > > Thanks, > > Shaobo Huang > > > =E4=BF=A1=E6=81=AF=E5=AE=89=E5=85=A8=E5=A3=B0=E6=98=8E=EF=BC=9A=E6=9C=AC= =E9=82=AE=E4=BB=B6=E5=8C=85=E5=90=AB=E4=BF=A1=E6=81=AF=E5=BD=92=E5=8F=91=E4= =BB=B6=E4=BA=BA=E6=89=80=E5=9C=A8=E7=BB=84=E7=BB=87=E6=89=80=E6=9C=89,=E5= =8F=91=E4=BB=B6=E4=BA=BA=E6=89=80=E5=9C=A8=E7=BB=84=E7=BB=87=E5=AF=B9=E8=AF= =A5=E9=82=AE=E4=BB=B6=E6=8B=A5=E6=9C=89=E6=89=80=E6=9C=89=E6=9D=83=E5=88=A9= =E3=80=82=E8=AF=B7=E6=8E=A5=E6=94=B6=E8=80=85=E6=B3=A8=E6=84=8F=E4=BF=9D=E5= =AF=86,=E6=9C=AA=E7=BB=8F=E5=8F=91=E4=BB=B6=E4=BA=BA=E4=B9=A6=E9=9D=A2=E8= =AE=B8=E5=8F=AF,=E4=B8=8D=E5=BE=97=E5=90=91=E4=BB=BB=E4=BD=95=E7=AC=AC=E4= =B8=89=E6=96=B9=E7=BB=84=E7=BB=87=E5=92=8C=E4=B8=AA=E4=BA=BA=E9=80=8F=E9=9C= =B2=E6=9C=AC=E9=82=AE=E4=BB=B6=E6=89=80=E5=90=AB=E4=BF=A1=E6=81=AF=E3=80=82 > Information Security Notice: The information contained in this mail is so= lely property of the sender's organization.This mail communication is confi= dential.Recipients named above are obligated to maintain secrecy and are no= t permitted to disclose the contents of this communication to others. Just to confirm that I can reproduce this. Sudeep will be back in a few days, in case he has more background or another view on the topic, but I agree asymmetric _LPI states should ideally be visible to the kernel. I am having a look at the code aswell. In case you have an implementation, I can provide additional testing. Regards, Pierre IMPORTANT NOTICE: The contents of this email and any attachments are confid= ential and may also be privileged. If you are not the intended recipient, p= lease notify the sender immediately and do not disclose the contents to any= other person, use it for any purpose, or store or copy the information in = any medium. Thank you.