[RFC PATCH v2 2/2] DEBUG: workqueue: kworker spawner

[Valentin Schneider <vschneid@redhat.com>]

---
 kernel/Makefile    |  2 +-
 kernel/workqueue.c |  9 +++++-
 kernel/wqstress.c  | 69 ++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 78 insertions(+), 2 deletions(-)
 create mode 100644 kernel/wqstress.c

diff --git a/kernel/Makefile b/kernel/Makefile
index a7e1f49ab2b3..860133f7bca5 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -10,7 +10,7 @@ obj-y     = fork.o exec_domain.o panic.o \
 	    extable.o params.o platform-feature.o \
 	    kthread.o sys_ni.o nsproxy.o \
 	    notifier.o ksysfs.o cred.o reboot.o \
-	    async.o range.o smpboot.o ucount.o regset.o
+	    async.o range.o smpboot.o ucount.o regset.o wqstress.o
 
 obj-$(CONFIG_USERMODE_DRIVER) += usermode_driver.o
 obj-$(CONFIG_MODULES) += kmod.o
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 27642166dcc5..9559d0256683 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -91,7 +91,7 @@ enum {
 	BUSY_WORKER_HASH_ORDER	= 6,		/* 64 pointers */
 
 	MAX_IDLE_WORKERS_RATIO	= 4,		/* 1/4 of busy can be idle */
-	IDLE_WORKER_TIMEOUT	= 300 * HZ,	/* keep idle ones for 5 mins */
+	IDLE_WORKER_TIMEOUT	= 3 * HZ,	/* keep idle ones for 5 mins */
 
 	MAYDAY_INITIAL_TIMEOUT  = HZ / 100 >= 2 ? HZ / 100 : 2,
 						/* call for help after 10ms
@@ -1988,6 +1988,10 @@ static void rebind_worker(struct worker *worker, struct worker_pool *pool)
 
 static void reap_worker(struct worker *worker)
 {
+	pr_info("WORKER_REAP: task=%s cpu=%d this_task=%s this_cpu=%d\n",
+		worker->task->comm, task_cpu(worker->task),
+		current->comm, raw_smp_processor_id());
+
 	list_del_init(&worker->entry);
 	unbind_worker(worker);
 	wake_up_process(worker->task);
@@ -2443,6 +2447,9 @@ static int worker_thread(void *__worker)
 		WARN_ON_ONCE(!list_empty(&worker->entry));
 		set_pf_worker(false);
 
+		pr_info("WORKER_DIE: task=%s this_cpu=%d\n",
+			current->comm, raw_smp_processor_id());
+
 		set_task_comm(worker->task, "kworker/dying");
 		ida_free(&pool->worker_ida, worker->id);
 		worker_detach_from_pool(worker);
diff --git a/kernel/wqstress.c b/kernel/wqstress.c
new file mode 100644
index 000000000000..16a3771027cd
--- /dev/null
+++ b/kernel/wqstress.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/sched.h>
+
+MODULE_AUTHOR("Valentin Schneider <vschneid@redhat.com>");
+MODULE_LICENSE("GPL");
+
+#define TARGET_CPU 3
+
+static void wqstress_workfn(struct work_struct *work)
+{
+	schedule_timeout_interruptible(10 * HZ);
+}
+
+#define DECL_WORK(n) static DECLARE_WORK(wqstress_work_##n, wqstress_workfn)
+#define KICK_WORK(n) do {						\
+		schedule_work_on(TARGET_CPU, &wqstress_work_##n);	\
+	} while (0);
+#define FLUSH_WORK(n) do {			\
+		flush_work(&wqstress_work_##n);	\
+	} while (0);
+
+DECL_WORK(0);
+DECL_WORK(1);
+DECL_WORK(2);
+DECL_WORK(3);
+DECL_WORK(4);
+DECL_WORK(5);
+DECL_WORK(6);
+DECL_WORK(7);
+DECL_WORK(8);
+DECL_WORK(9);
+
+/*
+ * This should create ≈(N-1) extra kworkers for N kicked work
+ */
+static int __init wqstress_init(void)
+{
+	pr_info("WQSTRESS START\n");
+
+	sched_set_fifo_low(current);
+
+	KICK_WORK(0);
+	KICK_WORK(1);
+	KICK_WORK(2);
+	KICK_WORK(3);
+	KICK_WORK(4);
+	KICK_WORK(5);
+	KICK_WORK(6);
+	KICK_WORK(7);
+	KICK_WORK(8);
+	KICK_WORK(9);
+
+	FLUSH_WORK(0);
+	FLUSH_WORK(1);
+	FLUSH_WORK(2);
+	FLUSH_WORK(3);
+	FLUSH_WORK(4);
+	FLUSH_WORK(5);
+	FLUSH_WORK(6);
+	FLUSH_WORK(7);
+	FLUSH_WORK(8);
+	FLUSH_WORK(9);
+
+	return 0;
+}
+
+late_initcall_sync(wqstress_init);
-- 
2.31.1