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X-OriginatorOrg: amd.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 18 Dec 2024 04:40:22.5066 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 5aec189b-cc98-4fe6-7b15-08dd1f1e1573 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=[SATLEXMB04.amd.com] X-MS-Exchange-CrossTenant-AuthSource: SA2PEPF0000150B.namprd04.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: SN7PR12MB8771 Content-Type: text/plain; charset="utf-8" From: Peter Zijlstra In /proc/schedstat, lb_hot_gained reports the number hot tasks pulled during load balance. This value is incremented in can_migrate_task() if the task is migratable and hot. After incrementing the value, load balancer can still decide not to migrate this task leading to wrong accounting. Fix this by incrementing stats when hot tasks are detached. This issue only exists in detach_tasks() where we can decide to not migrate hot task even if it is migratable. However, in detach_one_task(), we migrate it unconditionally. Link: https://lore.kernel.org/all/20230619092228.GK4253@hirez.programming.k= icks-ass.net/ [Swapnil: Handled the case where nr_failed_migrations_hot was not accounted= properly and wrote commit log] Fixes: d31980846f96 ("sched: Move up affinity check to mitigate useless red= oing overhead") Reported-by: Gautham R. Shenoy Not-yet-signed-off-by: Peter Zijlstra Signed-off-by: Swapnil Sapkal --- include/linux/sched.h | 1 + kernel/sched/fair.c | 17 +++++++++++++---- 2 files changed, 14 insertions(+), 4 deletions(-) diff --git a/include/linux/sched.h b/include/linux/sched.h index 1d5cc3e50884..cf798d4e3ca6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -937,6 +937,7 @@ struct task_struct { unsigned sched_reset_on_fork:1; unsigned sched_contributes_to_load:1; unsigned sched_migrated:1; + unsigned sched_task_hot:1; =20 /* Force alignment to the next boundary: */ unsigned :0; diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 3356315d7e64..baefbf1b07fd 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9354,6 +9354,8 @@ int can_migrate_task(struct task_struct *p, struct lb= _env *env) int tsk_cache_hot; =20 lockdep_assert_rq_held(env->src_rq); + if (p->sched_task_hot) + p->sched_task_hot =3D 0; =20 /* * We do not migrate tasks that are: @@ -9426,10 +9428,8 @@ int can_migrate_task(struct task_struct *p, struct l= b_env *env) =20 if (tsk_cache_hot <=3D 0 || env->sd->nr_balance_failed > env->sd->cache_nice_tries) { - if (tsk_cache_hot =3D=3D 1) { - schedstat_inc(env->sd->lb_hot_gained[env->idle]); - schedstat_inc(p->stats.nr_forced_migrations); - } + if (tsk_cache_hot =3D=3D 1) + p->sched_task_hot =3D 1; return 1; } =20 @@ -9444,6 +9444,12 @@ static void detach_task(struct task_struct *p, struc= t lb_env *env) { lockdep_assert_rq_held(env->src_rq); =20 + if (p->sched_task_hot) { + p->sched_task_hot =3D 0; + schedstat_inc(env->sd->lb_hot_gained[env->idle]); + schedstat_inc(p->stats.nr_forced_migrations); + } + deactivate_task(env->src_rq, p, DEQUEUE_NOCLOCK); set_task_cpu(p, env->dst_cpu); } @@ -9604,6 +9610,9 @@ static int detach_tasks(struct lb_env *env) =20 continue; next: + if (p->sched_task_hot) + schedstat_inc(p->stats.nr_failed_migrations_hot); + list_move(&p->se.group_node, tasks); } =20 --=20 2.43.0