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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: z8IONpDhdJIsPcESL0tYfPccMTT9K0PIYx0mHLkLumZS3XK05nMyL/b5w6+RV7p5Pxpjw4bht5O+ooFuQc3XD9kVyinRF63C0TbmRJZSu+1k99jVSzrg1riIspblHLZZMiV46vcHPVT1v2H4eHnYNk4P/zzTa/eNZS8dHDawlNTwjVgb2vK5wqLMbhGHDdFYRWtX7vGgeCPrASCZoITq6uL2Fmm/g5TxOCOnAaQZCLgR/TgTi7WCUOGbsIukczKZwdJSaau74B+B8uZt+ewrvY5C1y247Yv/BMC7P6GtPtviRxQtRlcH0xwc94FaHYSP390RQGyNYSRSeMRkwxEEswrNVrB5koE1g6tHxW6CsFJhbGul+W7t5B1/1J9tVkQIfKXlP2Qu6Cs3T/8us05BEKCoT5i7Mbu4l4I/QizP4kwM76nEA+Kbw1zLgPOLHAvE X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 Feb 2026 09:42:07.9448 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 9085bb17-eb6d-4535-781a-08de6563fe98 X-MS-Exchange-CrossTenant-Id: 3dd8961f-e488-4e60-8e11-a82d994e183d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=3dd8961f-e488-4e60-8e11-a82d994e183d;Ip=[165.204.84.17];Helo=[satlexmb08.amd.com] X-MS-Exchange-CrossTenant-AuthSource: CO1PEPF000075F0.namprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DS0PR12MB7927 Hello Pierre, On 2/5/2026 8:38 PM, Pierre Gondois wrote: > Halving the imbalance currently lead to the following scenario. > On a Juno with 2 clusters: CLU0: 4 CPUs and CLU1: 2 CPUs, with > 6 long running tasks: > - 1 task on the 2-CPUs cluster > - 5 Tasks run in the 4-CPUs cluster > Running the load balancer from the idle CPU (in CLU1): > - Local group: CLU1: idle_cpus=1; nr_running=1; type=group_has_spare > - Busiest group: CLU0 idle_cpus=0; nr_running=5 type=group_overloaded > Half of (local->idle_cpus - busiest->idle_cpus) is 0. > No task is migrated and the task placement persists. ... > --- > kernel/sched/fair.c | 10 ++++------ > 1 file changed, 4 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index aa14a9982b9f1..9dac3536d9c19 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -11235,20 +11235,18 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s > return; > } > > - if (busiest->group_weight == 1 || sds->prefer_sibling) { > + env->migration_type = migrate_task; > + if (busiest->group_weight == 1 || sds->prefer_sibling || !busiest->idle_cpus) { I suppose you also have SD_ASYM_CPUCAPACITY set on your sd which is why "sds->prefer_sibling" is false here. Instead of checking for "busiest->idle_cpus", would it make sense to enter this case for sibling_imbalance() when we have: capacity_greater(capacity_of(env->dst_cpu), sds->busiest->sgc->min_capacity) since it could very well be the case that the smaller cluster is actually idle since task_fits_cpu() returned false for CPUs there? I couldn't actually spot any case where we compare the capacities of local and busiest group for <= fully_loaded but let me know if I've missed something. > /* > - * When prefer sibling, evenly spread running tasks on > - * groups. > + * When prefer sibling, or when busiest has no idle CPU, > + * evenly spread running tasks on groups. > */ > - env->migration_type = migrate_task; > env->imbalance = sibling_imbalance(env, sds, busiest, local); I'm slightly skeptical of spreading the tasks evenly without considering the capacity difference when we are on SD_ASYM_CPUCAPACITY. I suppose we'll filter out the target in sched_balance_find_src_rq() and bail out if we have only see lower capacity CPUs on the busiest group. > } else { > - > /* > * If there is no overload, we just want to even the number of > * idle CPUs. > */ > - env->migration_type = migrate_task; > env->imbalance = local->idle_cpus; > lsub_positive(&env->imbalance, busiest->idle_cpus); > } -- Thanks and Regards, Prateek