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charset="utf-8" When a concurrency-managed per-CPU work item runs continuously without sleeping for longer than wq_cpu_intensive_thresh_us, wq_worker_tick() marks the worker as WORKER_CPU_INTENSIVE and kicks it out of concurrency management so that pending work items on the pool are not starved. While CONFIG_WQ_CPU_INTENSIVE_REPORT logs rate-limited warnings and pwq->stats[PWQ_STAT_CPU_INTENSIVE] maintains a cumulative counter, there is currently no tracepoint emitted at the moment of this transition. Therefore, add the workqueue_cpu_intensive tracepoint, recording the work_struct pointer and callback function pointer, workqueue name, executing CPU, and the runtime duration consumed in microseconds. This enables eBPF profilers, bpftrace, and Ftrace to immediately detect and attribute CPU-hogging work items in real time. Signed-off-by: Aaron Tomlin --- include/trace/events/workqueue.h | 40 ++++++++++++++++++++++++++++++++ kernel/workqueue.c | 7 ++++++ 2 files changed, 47 insertions(+) diff --git a/include/trace/events/workqueue.h b/include/trace/events/workqu= eue.h index b0de2bc9ed52..d2ad38f93a83 100644 --- a/include/trace/events/workqueue.h +++ b/include/trace/events/workqueue.h @@ -126,7 +126,47 @@ TRACE_EVENT(workqueue_execute_end, TP_printk("work struct %p: function %ps", __entry->work, __entry->functio= n) ); =20 +/** + * workqueue_cpu_intensive - called when a work item exceeds cpu_intensive= threshold + * @pwq: pointer to struct pool_workqueue + * @work: pointer to struct work_struct + * @function: pointer to worker function + * @duration_us: CPU time consumed in microseconds + * + * This event occurs when a concurrency-managed work item runs for longer + * than wq_cpu_intensive_thresh_us without sleeping and is excluded from + * concurrency management to prevent stalling other work items. + */ +TRACE_EVENT(workqueue_cpu_intensive, + + TP_PROTO(struct pool_workqueue *pwq, struct work_struct *work, + work_func_t function, u64 duration_us), + + TP_ARGS(pwq, work, function, duration_us), + + TP_STRUCT__entry( + __field( void *, work ) + __field( void *, function ) + __string( workqueue, pwq->wq->name ) + __field( int, cpu ) + __field( u64, duration_us ) + ), + + TP_fast_assign( + __entry->work =3D work; + __entry->function =3D function; + __assign_str(workqueue); + __entry->cpu =3D pwq->pool->cpu; + __entry->duration_us =3D duration_us; + ), + + TP_printk("work struct=3D%p function=3D%ps workqueue=3D%s cpu=3D%d durati= on_us=3D%llu", + __entry->work, __entry->function, __get_str(workqueue), + __entry->cpu, __entry->duration_us) +); + #endif /* _TRACE_WORKQUEUE_H */ =20 /* This part must be outside protection */ #include + diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 3c034cbc5bb3..bad1217cf45a 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -56,6 +56,7 @@ #include #include #include +#include =20 #include "workqueue_internal.h" =20 @@ -1532,6 +1533,7 @@ void wq_worker_tick(struct task_struct *task) struct worker *worker =3D kthread_data(task); struct pool_workqueue *pwq =3D worker->current_pwq; struct worker_pool *pool =3D worker->pool; + u64 delta; =20 if (!pwq) return; @@ -1572,6 +1574,11 @@ void wq_worker_tick(struct task_struct *task) pwq->stats[PWQ_STAT_CM_WAKEUP]++; 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charset="utf-8" When a worker pool fails to create a new worker thread within MAYDAY_INTERVAL (e.g., typically under severe memory pressure where memory reclaim paths depend on pending work items), send_mayday() signals distress to the workqueue's rescuer thread. The rescuer then takes over processing the pending work items via assign_rescuer_work(). While pwq->stats[PWQ_STAT_MAYDAY] and pwq->stats[PWQ_STAT_RESCUED] track these occurrences cumulatively, there is currently no event-driven mechanism to observe exactly when mayday distress occurs or which work items require rescue. Add two new tracepoints namely workqueue_mayday and workqueue_rescued to make distress and rescuer execution easily observable (e.g., via Ftrace or eBPF). Signed-off-by: Aaron Tomlin --- include/trace/events/workqueue.h | 68 ++++++++++++++++++++++++++++++++ kernel/workqueue.c | 2 + 2 files changed, 70 insertions(+) diff --git a/include/trace/events/workqueue.h b/include/trace/events/workqu= eue.h index d2ad38f93a83..12ac24586835 100644 --- a/include/trace/events/workqueue.h +++ b/include/trace/events/workqueue.h @@ -165,6 +165,74 @@ TRACE_EVENT(workqueue_cpu_intensive, __entry->cpu, __entry->duration_us) ); =20 +/** + * workqueue_mayday - called when a pool_workqueue sends mayday to rescuer + * @pwq: pointer to struct pool_workqueue + * + * This event occurs when a worker pool fails to create a new worker + * within MAYDAY_INTERVAL and requests the workqueue's rescuer thread to + * process pending works. + */ +TRACE_EVENT(workqueue_mayday, + + TP_PROTO(struct pool_workqueue *pwq), + + TP_ARGS(pwq), + + TP_STRUCT__entry( + __string( workqueue, pwq->wq->name ) + __field( int, pool_id ) + __field( int, cpu ) + __field( int, nr_active ) + ), + + TP_fast_assign( + __assign_str(workqueue); + __entry->pool_id =3D pwq->pool->id; + __entry->cpu =3D pwq->pool->cpu; + __entry->nr_active =3D pwq->nr_active; + ), + + TP_printk("workqueue=3D%s pool_id=3D%d cpu=3D%d nr_active=3D%d", + __get_str(workqueue), __entry->pool_id, __entry->cpu, + __entry->nr_active) +); + +/** + * workqueue_rescued - called when a work item is assigned to a rescuer + * @pwq: pointer to struct pool_workqueue + * @work: pointer to struct work_struct + * @function: pointer to worker function + * + * This event occurs when a work item is claimed by a rescuer thread + * to guarantee forward progress. + */ +TRACE_EVENT(workqueue_rescued, + + TP_PROTO(struct pool_workqueue *pwq, struct work_struct *work, + work_func_t function), + + TP_ARGS(pwq, work, function), + + TP_STRUCT__entry( + __field( void *, work ) + __field( void *, function ) + __string( workqueue, pwq->wq->name ) + __field( int, cpu ) + ), + + TP_fast_assign( + __entry->work =3D work; + __entry->function =3D function; + __assign_str(workqueue); + __entry->cpu =3D pwq->pool->cpu; + ), + + TP_printk("work struct=3D%p function=3D%ps workqueue=3D%s cpu=3D%d", + __entry->work, __entry->function, __get_str(workqueue), + __entry->cpu) +); + #endif /* _TRACE_WORKQUEUE_H */ =20 /* This part must be outside protection */ diff --git a/kernel/workqueue.c b/kernel/workqueue.c index bad1217cf45a..ab1371ed890a 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3124,6 +3124,7 @@ static void send_mayday(struct pool_workqueue *pwq) list_add_tail(&pwq->mayday_node, &wq->maydays); wake_up_process(wq->rescuer->task); pwq->stats[PWQ_STAT_MAYDAY]++; + trace_workqueue_mayday(pwq); } } =20 @@ -3621,6 +3622,7 @@ static bool assign_rescuer_work(struct pool_workqueue= *pwq, struct worker *rescu list_for_each_entry_safe_from(work, n, &pool->worklist, entry) { if (get_work_pwq(work) =3D=3D pwq && assign_work(work, rescuer, &n)) { pwq->stats[PWQ_STAT_RESCUED]++; + trace_workqueue_rescued(pwq, work, work->func); /* put the cursor for next search */ list_move_tail(&cursor->entry, &n->entry); 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charset="utf-8" Bottom-Half (BH) workqueues execute work items in softirq context. To prevent softirqs from starving user and kernel threads, bh_worker() enforces execution limits (i.e., BH_WORKER_JIFFIES and BH_WORKER_RESTARTS). When keep_working() is still true but either the time slice or restart count is exhausted, bh_worker() yields execution and re-raises the softirq via kick_bh_pool(). Currently, there is no observability into when a BH worker hits these limits and is forced to yield. Add the workqueue_bh_budget_yield tracepoint, emitted when bh_worker() exits the processing loop with pending work items remaining. It records, the worker pool ID, executing CPU, number of loop restarts consumed, a boolean flag indicating whether the yield was due to a time slice timeout, and a boolean flag indicating whether this is a high-priority BH pool. Signed-off-by: Aaron Tomlin --- include/trace/events/workqueue.h | 39 ++++++++++++++++++++++++++++++++ kernel/workqueue.c | 26 +++++++++++++++++++-- 2 files changed, 63 insertions(+), 2 deletions(-) diff --git a/include/trace/events/workqueue.h b/include/trace/events/workqu= eue.h index 12ac24586835..bbba34e40470 100644 --- a/include/trace/events/workqueue.h +++ b/include/trace/events/workqueue.h @@ -9,6 +9,7 @@ #include =20 struct pool_workqueue; +struct worker_pool; =20 /** * workqueue_queue_work - called when a work gets queued @@ -233,6 +234,44 @@ TRACE_EVENT(workqueue_rescued, __entry->cpu) ); =20 +/** + * workqueue_bh_budget_yield - called when a BH worker yields due to budge= t exhaustion + * @pool: pointer to struct worker_pool + * @restarts: number of restarts executed + * @timeout: whether execution hit the time limit (BH_WORKER_JIFFIES) + * @highpri: whether this is a high-priority BH pool + * + * This event occurs when a bottom-half (BH) worker pool running in softirq + * context exhausts its execution time slice or restart limit and must yie= ld + * execution. + */ +TRACE_EVENT(workqueue_bh_budget_yield, + + TP_PROTO(struct worker_pool *pool, int restarts, bool timeout, bool highp= ri), + + TP_ARGS(pool, restarts, timeout, highpri), + + TP_STRUCT__entry( + __field( int, pool_id ) + __field( int, cpu ) + __field( int, restarts ) + __field( bool, timeout ) + __field( bool, highpri ) + ), + + TP_fast_assign( + __entry->pool_id =3D pool->id; + __entry->cpu =3D pool->cpu; + __entry->restarts =3D restarts; + __entry->timeout =3D timeout; + __entry->highpri =3D highpri; + ), + + TP_printk("pool_id=3D%d cpu=3D%d restarts=3D%d timeout=3D%d highpri=3D%d", + __entry->pool_id, __entry->cpu, __entry->restarts, + __entry->timeout, __entry->highpri) +); + #endif /* _TRACE_WORKQUEUE_H */ =20 /* This part must be outside protection */ diff --git a/kernel/workqueue.c b/kernel/workqueue.c index ab1371ed890a..74f595396227 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3758,6 +3758,9 @@ static void bh_worker(struct worker *worker) struct worker_pool *pool =3D worker->pool; int nr_restarts =3D BH_WORKER_RESTARTS; unsigned long end =3D jiffies + BH_WORKER_JIFFIES; + bool budget_exhausted =3D false; + bool timeout =3D false; + int restarts =3D 0; =20 worker_lock_callback(pool); raw_spin_lock_irq(&pool->lock); @@ -3780,8 +3783,23 @@ static void bh_worker(struct worker *worker) =20 if (assign_work(work, worker, NULL)) process_scheduled_works(worker); - } while (keep_working(pool) && - --nr_restarts && time_before(jiffies, end)); + + if (!keep_working(pool)) + break; + + if (!--nr_restarts) { + budget_exhausted =3D true; + break; + } + + if (!time_before(jiffies, end)) { + budget_exhausted =3D true; + timeout =3D true; + break; + } + + restarts++; + } while (1); =20 worker_set_flags(worker, WORKER_PREP); done: @@ -3789,6 +3807,10 @@ static void bh_worker(struct worker *worker) kick_pool(pool); raw_spin_unlock_irq(&pool->lock); worker_unlock_callback(pool); + + if (budget_exhausted) + trace_workqueue_bh_budget_yield(pool, restarts, timeout, + pool->attrs->nice =3D=3D HIGHPRI_NICE_LEVEL); } =20 /* --=20 2.55.0