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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Sep 2025 08:55:30.1874 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: f66447a9-6f42-434d-0652-08ddfa7ef2c5 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=[satlexmb07.amd.com] X-MS-Exchange-CrossTenant-AuthSource: BN2PEPF00004FC0.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: DM4PR12MB7549 Hello Fernand, On 9/22/2025 6:09 PM, Fernand Sieber wrote: > The fast path in select_idle_sibling() can place tasks on CPUs without > considering core scheduling constraints, potentially causing immediate > force idle when the sibling runs an incompatible task. > > Add cookie compatibility checks before selecting a CPU in the fast path. > This prevents placing waking tasks on CPUs where the sibling is running > an incompatible task, reducing force idle occurrences. > > Signed-off-by: Fernand Sieber > --- > kernel/sched/fair.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > index 78b36225a039..a9cbb0e9bb43 100644 > --- a/kernel/sched/fair.c > +++ b/kernel/sched/fair.c > @@ -7578,7 +7578,7 @@ static int select_idle_smt(struct task_struct *p, struct sched_domain *sd, int t > */ > if (!cpumask_test_cpu(cpu, sched_domain_span(sd))) > continue; > - if (available_idle_cpu(cpu) || sched_idle_cpu(cpu)) > + if (__select_idle_cpu(cpu, p) != -1) So with Patch 1, you already check for cookie matching while entering select_idle_smt() and now, each pass of the loop again does a sched_core_cookie_match() which internally loops through the smt mask again! Seems wasteful. > return cpu; > } > > @@ -7771,7 +7771,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > */ > lockdep_assert_irqs_disabled(); > > - if ((available_idle_cpu(target) || sched_idle_cpu(target)) && > + if ((__select_idle_cpu(target, p) != -1) && > asym_fits_cpu(task_util, util_min, util_max, target)) > return target; > > @@ -7779,7 +7779,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > * If the previous CPU is cache affine and idle, don't be stupid: > */ > if (prev != target && cpus_share_cache(prev, target) && > - (available_idle_cpu(prev) || sched_idle_cpu(prev)) && > + (__select_idle_cpu(prev, p) != -1) && > asym_fits_cpu(task_util, util_min, util_max, prev)) { > > if (!static_branch_unlikely(&sched_cluster_active) || > @@ -7811,7 +7811,7 @@ static int select_idle_sibling(struct task_struct *p, int prev, int target) > if (recent_used_cpu != prev && > recent_used_cpu != target && > cpus_share_cache(recent_used_cpu, target) && > - (available_idle_cpu(recent_used_cpu) || sched_idle_cpu(recent_used_cpu)) && > + (__select_idle_cpu(recent_used_cpu, p) != -1) && On an SMT-8 system, all the looping over smt mask per wakeup will add up. Is that not a concern? A single task with core cookie enabled will add massive overhead for all wakeup in the system. > cpumask_test_cpu(recent_used_cpu, p->cpus_ptr) && > asym_fits_cpu(task_util, util_min, util_max, recent_used_cpu)) { > -- Thanks and Regards, Prateek