From f630c7c6f10546ebff15c3a856e7949feb7a2372 Mon Sep 17 00:00:00 2001 From: Rob Clark Date: Mon, 14 Dec 2020 19:03:14 -0800 Subject: kthread: add kthread_work tracepoints While migrating some code from wq to kthread_worker, I found that I missed the execute_start/end tracepoints. So add similar tracepoints for kthread_work. And for completeness, queue_work tracepoint (although this one differs slightly from the matching workqueue tracepoint). Link: https://lkml.kernel.org/r/20201010180323.126634-1-robdclark@gmail.com Signed-off-by: Rob Clark Cc: Rob Clark Cc: Steven Rostedt Cc: Ingo Molnar Cc: "Peter Zijlstra (Intel)" Cc: Phil Auld Cc: Valentin Schneider Cc: Thara Gopinath Cc: Randy Dunlap Cc: Vincent Donnefort Cc: Mel Gorman Cc: Jens Axboe Cc: Marcelo Tosatti Cc: Frederic Weisbecker Cc: Ilias Stamatis Cc: Liang Chen Cc: Ben Dooks Cc: Peter Zijlstra Cc: "J. Bruce Fields" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kthread.c | 9 +++++++++ 1 file changed, 9 insertions(+) (limited to 'kernel/kthread.c') diff --git a/kernel/kthread.c b/kernel/kthread.c index 933a625621b8..34516b0a6eb7 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -704,8 +704,15 @@ repeat: raw_spin_unlock_irq(&worker->lock); if (work) { + kthread_work_func_t func = work->func; __set_current_state(TASK_RUNNING); + trace_sched_kthread_work_execute_start(work); work->func(work); + /* + * Avoid dereferencing work after this point. The trace + * event only cares about the address. + */ + trace_sched_kthread_work_execute_end(work, func); } else if (!freezing(current)) schedule(); @@ -834,6 +841,8 @@ static void kthread_insert_work(struct kthread_worker *worker, { kthread_insert_work_sanity_check(worker, work); + trace_sched_kthread_work_queue_work(worker, work); + list_add_tail(&work->node, pos); work->worker = worker; if (!worker->current_work && likely(worker->task)) -- cgit v1.2.3 From ebb2bdcef8a00d59b27d3532c423110559821e1d Mon Sep 17 00:00:00 2001 From: Petr Mladek Date: Mon, 14 Dec 2020 19:03:18 -0800 Subject: kthread_worker: document CPU hotplug handling The kthread worker API is simple. In short, it allows to create, use, and destroy workers. kthread_create_worker_on_cpu() just allows to bind a newly created worker to a given CPU. It is up to the API user how to handle CPU hotplug. They have to decide how to handle pending work items, prevent queuing new ones, and restore the functionality when the CPU goes off and on. There are few catches: + The CPU affinity gets lost when it is scheduled on an offline CPU. + The worker might not exist when the CPU was off when the user created the workers. A good practice is to implement two CPU hotplug callbacks and destroy/create the worker when CPU goes down/up. Mention this in the function description. [akpm@linux-foundation.org: grammar tweaks] Link: https://lore.kernel.org/r/20201028073031.4536-1-qiang.zhang@windriver.com Link: https://lkml.kernel.org/r/20201102101039.19227-1-pmladek@suse.com Reported-by: Zhang Qiang Signed-off-by: Petr Mladek Cc: Tejun Heo Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- kernel/kthread.c | 20 +++++++++++++++++++- 1 file changed, 19 insertions(+), 1 deletion(-) (limited to 'kernel/kthread.c') diff --git a/kernel/kthread.c b/kernel/kthread.c index 34516b0a6eb7..97e053ade74a 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -793,7 +793,25 @@ EXPORT_SYMBOL(kthread_create_worker); * A good practice is to add the cpu number also into the worker name. * For example, use kthread_create_worker_on_cpu(cpu, "helper/%d", cpu). * - * Returns a pointer to the allocated worker on success, ERR_PTR(-ENOMEM) + * CPU hotplug: + * The kthread worker API is simple and generic. It just provides a way + * to create, use, and destroy workers. + * + * It is up to the API user how to handle CPU hotplug. They have to decide + * how to handle pending work items, prevent queuing new ones, and + * restore the functionality when the CPU goes off and on. There are a + * few catches: + * + * - CPU affinity gets lost when it is scheduled on an offline CPU. + * + * - The worker might not exist when the CPU was off when the user + * created the workers. + * + * Good practice is to implement two CPU hotplug callbacks and to + * destroy/create the worker when the CPU goes down/up. + * + * Return: + * The pointer to the allocated worker on success, ERR_PTR(-ENOMEM) * when the needed structures could not get allocated, and ERR_PTR(-EINTR) * when the worker was SIGKILLed. */ -- cgit v1.2.3