spl-taskq: per-taskq kstats

This exposes a variety of per-taskq stats under /proc/spl/kstat/taskq,
one file per taskq, named for the taskq name.instance.

These include a small amount of info about the taskq config, the current
state of the threads and queues, and various counters for thread and
queue activity since the taskq was created.

To assist with decrementing queue size counters, the list an entry is on
is encoded in spare bits in the entry flags.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Sponsored-by: Klara, Inc.
Sponsored-by: Syneto
Closes #16171

include/os/linux/spl/sys/taskq.h

@@ -20,6 +20,10 @@
  *  You should have received a copy of the GNU General Public License along
  *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
  */
+/*
+ * Copyright (c) 2024, Klara Inc.
+ * Copyright (c) 2024, Syneto
+ */
 
 #ifndef _SPL_TASKQ_H
 #define	_SPL_TASKQ_H
@@ -33,6 +37,9 @@
 #include <sys/thread.h>
 #include <sys/rwlock.h>
 #include <sys/wait.h>
+#include <sys/wmsum.h>
+
+typedef struct kstat_s kstat_t;
 
 #define	TASKQ_NAMELEN		31
 
@@ -74,6 +81,32 @@ typedef enum tq_lock_role {
 typedef unsigned long taskqid_t;
 typedef void (task_func_t)(void *);
 
+typedef struct taskq_sums {
+	/* gauges (inc/dec counters, current value) */
+	wmsum_t tqs_threads_active;		/* threads running a task */
+	wmsum_t tqs_threads_idle;		/* threads waiting for work */
+	wmsum_t tqs_threads_total;		/* total threads */
+	wmsum_t tqs_tasks_pending;		/* tasks waiting to execute */
+	wmsum_t tqs_tasks_priority;		/* hi-pri tasks waiting */
+	wmsum_t tqs_tasks_total;		/* total waiting tasks */
+	wmsum_t tqs_tasks_delayed;		/* tasks deferred to future */
+	wmsum_t tqs_entries_free;		/* task entries on free list */
+
+	/* counters (inc only, since taskq creation) */
+	wmsum_t tqs_threads_created;		/* threads created */
+	wmsum_t tqs_threads_destroyed;		/* threads destroyed */
+	wmsum_t tqs_tasks_dispatched;		/* tasks dispatched */
+	wmsum_t tqs_tasks_dispatched_delayed;	/* tasks delayed to future */
+	wmsum_t tqs_tasks_executed_normal;	/* normal pri tasks executed */
+	wmsum_t tqs_tasks_executed_priority;	/* high pri tasks executed */
+	wmsum_t tqs_tasks_executed;		/* total tasks executed */
+	wmsum_t tqs_tasks_delayed_requeued;	/* delayed tasks requeued */
+	wmsum_t tqs_tasks_cancelled;		/* tasks cancelled before run */
+	wmsum_t tqs_thread_wakeups;		/* total thread wakeups */
+	wmsum_t tqs_thread_wakeups_nowork;	/* thread woken but no tasks */
+	wmsum_t tqs_thread_sleeps;		/* total thread sleeps */
+} taskq_sums_t;
+
 typedef struct taskq {
 	spinlock_t		tq_lock;	/* protects taskq_t */
 	char			*tq_name;	/* taskq name */
@@ -105,6 +138,8 @@ typedef struct taskq {
 	struct hlist_node	tq_hp_cb_node;
 	boolean_t		tq_hp_support;
 	unsigned long		lastspawnstop;	/* when to purge dynamic */
+	taskq_sums_t		tq_sums;
+	kstat_t			*tq_ksp;
 } taskq_t;
 
 typedef struct taskq_ent {
@@ -123,6 +158,13 @@ typedef struct taskq_ent {
 #define	TQENT_FLAG_PREALLOC	0x1
 #define	TQENT_FLAG_CANCEL	0x2
 
+/* bits 2-3 are which list tqent is on */
+#define	TQENT_LIST_NONE		0x0
+#define	TQENT_LIST_PENDING	0x4
+#define	TQENT_LIST_PRIORITY	0x8
+#define	TQENT_LIST_DELAY	0xc
+#define	TQENT_LIST_MASK		0xc
+
 typedef struct taskq_thread {
 	struct list_head	tqt_thread_list;
 	struct list_head	tqt_active_list;