Probes updates for v6.7:

- cleanups:
   . kprobes: Fixes typo in kprobes samples.
 
   . tracing/eprobes: Remove 'break' after return.
 
 - kretprobe/fprobe performance improvements:
   . lib: Introduce new `objpool`, which is a high performance lockless
     object queue. This uses per-cpu ring array to allocate/release
     objects from the pre-allocated object pool. Since the index of ring
     array is a 32bit sequential counter, we can retry to push/pop the
     object pointer from the ring without lock (as seq-lock does).
 
   . lib: Add an objpool test module to test the functionality and
     evaluate the performance under some circumstances.
 
   . kprobes/fprobe: Improve kretprobe and rethook scalability
     performance with objpool.
     This improves both legacy kretprobe and fprobe exit handler (which
     is based on rethook) to be scalable on SMP systems. Even with
     8-threads parallel test, it shows a great scalability improvement.
 
   . Remove unneeded freelist.h which is replaced by objpool.
 
   . objpool: Add maintainers entry for the objpool.
 
   . objpool: Fix to remove unused include header lines.
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Merge tag 'probes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace

Pull probes updates from Masami Hiramatsu:
 "Cleanups:

   - kprobes: Fixes typo in kprobes samples

   - tracing/eprobes: Remove 'break' after return

  kretprobe/fprobe performance improvements:

   - lib: Introduce new `objpool`, which is a high performance lockless
     object queue. This uses per-cpu ring array to allocate/release
     objects from the pre-allocated object pool.

     Since the index of ring array is a 32bit sequential counter, we can
     retry to push/pop the object pointer from the ring without lock (as
     seq-lock does)

   - lib: Add an objpool test module to test the functionality and
     evaluate the performance under some circumstances

   - kprobes/fprobe: Improve kretprobe and rethook scalability
     performance with objpool.

     This improves both legacy kretprobe and fprobe exit handler (which
     is based on rethook) to be scalable on SMP systems. Even with
     8-threads parallel test, it shows a great scalability improvement

   - Remove unneeded freelist.h which is replaced by objpool

   - objpool: Add maintainers entry for the objpool

   - objpool: Fix to remove unused include header lines"

* tag 'probes-v6.7' of git://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace:
  kprobes: unused header files removed
  MAINTAINERS: objpool added
  kprobes: freelist.h removed
  kprobes: kretprobe scalability improvement
  lib: objpool test module added
  lib: objpool added: ring-array based lockless MPMC
  tracing/eprobe: drop unneeded breaks
  samples: kprobes: Fixes a typo

lib/Kconfig.debug

@@ -2954,6 +2954,17 @@ config TEST_CLOCKSOURCE_WATCHDOG
 
 	  If unsure, say N.
 
+config TEST_OBJPOOL
+	tristate "Test module for correctness and stress of objpool"
+	default n
+	depends on m && DEBUG_KERNEL
+	help
+	  This builds the "test_objpool" module that should be used for
+	  correctness verification and concurrent testings of objects
+	  allocation and reclamation.
+
+	  If unsure, say N.
+
 endif # RUNTIME_TESTING_MENU
 
 config ARCH_USE_MEMTEST

lib/Makefile

@@ -34,7 +34,7 @@ lib-y := ctype.o string.o vsprintf.o cmdline.o \
 	 is_single_threaded.o plist.o decompress.o kobject_uevent.o \
 	 earlycpio.o seq_buf.o siphash.o dec_and_lock.o \
 	 nmi_backtrace.o win_minmax.o memcat_p.o \
-	 buildid.o
+	 buildid.o objpool.o
 
 lib-$(CONFIG_PRINTK) += dump_stack.o
 lib-$(CONFIG_SMP) += cpumask.o
@@ -107,6 +107,8 @@ obj-$(CONFIG_KPROBES_SANITY_TEST) += test_kprobes.o
 obj-$(CONFIG_TEST_REF_TRACKER) += test_ref_tracker.o
 CFLAGS_test_fprobe.o += $(CC_FLAGS_FTRACE)
 obj-$(CONFIG_FPROBE_SANITY_TEST) += test_fprobe.o
+obj-$(CONFIG_TEST_OBJPOOL) += test_objpool.o
+
 #
 # CFLAGS for compiling floating point code inside the kernel. x86/Makefile turns
 # off the generation of FPU/SSE* instructions for kernel proper but FPU_FLAGS

lib/objpool.c

@@ -0,0 +1,280 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/objpool.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/atomic.h>
+#include <linux/irqflags.h>
+#include <linux/cpumask.h>
+#include <linux/log2.h>
+
+/*
+ * objpool: ring-array based lockless MPMC/FIFO queues
+ *
+ * Copyright: wuqiang.matt@bytedance.com,mhiramat@kernel.org
+ */
+
+/* initialize percpu objpool_slot */
+static int
+objpool_init_percpu_slot(struct objpool_head *pool,
+			 struct objpool_slot *slot,
+			 int nodes, void *context,
+			 objpool_init_obj_cb objinit)
+{
+	void *obj = (void *)&slot->entries[pool->capacity];
+	int i;
+
+	/* initialize elements of percpu objpool_slot */
+	slot->mask = pool->capacity - 1;
+
+	for (i = 0; i < nodes; i++) {
+		if (objinit) {
+			int rc = objinit(obj, context);
+			if (rc)
+				return rc;
+		}
+		slot->entries[slot->tail & slot->mask] = obj;
+		obj = obj + pool->obj_size;
+		slot->tail++;
+		slot->last = slot->tail;
+		pool->nr_objs++;
+	}
+
+	return 0;
+}
+
+/* allocate and initialize percpu slots */
+static int
+objpool_init_percpu_slots(struct objpool_head *pool, int nr_objs,
+			  void *context, objpool_init_obj_cb objinit)
+{
+	int i, cpu_count = 0;
+
+	for (i = 0; i < pool->nr_cpus; i++) {
+
+		struct objpool_slot *slot;
+		int nodes, size, rc;
+
+		/* skip the cpu node which could never be present */
+		if (!cpu_possible(i))
+			continue;
+
+		/* compute how many objects to be allocated with this slot */
+		nodes = nr_objs / num_possible_cpus();
+		if (cpu_count < (nr_objs % num_possible_cpus()))
+			nodes++;
+		cpu_count++;
+
+		size = struct_size(slot, entries, pool->capacity) +
+			pool->obj_size * nodes;
+
+		/*
+		 * here we allocate percpu-slot & objs together in a single
+		 * allocation to make it more compact, taking advantage of
+		 * warm caches and TLB hits. in default vmalloc is used to
+		 * reduce the pressure of kernel slab system. as we know,
+		 * mimimal size of vmalloc is one page since vmalloc would
+		 * always align the requested size to page size
+		 */
+		if (pool->gfp & GFP_ATOMIC)
+			slot = kmalloc_node(size, pool->gfp, cpu_to_node(i));
+		else
+			slot = __vmalloc_node(size, sizeof(void *), pool->gfp,
+				cpu_to_node(i), __builtin_return_address(0));
+		if (!slot)
+			return -ENOMEM;
+		memset(slot, 0, size);
+		pool->cpu_slots[i] = slot;
+
+		/* initialize the objpool_slot of cpu node i */
+		rc = objpool_init_percpu_slot(pool, slot, nodes, context, objinit);
+		if (rc)
+			return rc;
+	}
+
+	return 0;
+}
+
+/* cleanup all percpu slots of the object pool */
+static void objpool_fini_percpu_slots(struct objpool_head *pool)
+{
+	int i;
+
+	if (!pool->cpu_slots)
+		return;
+
+	for (i = 0; i < pool->nr_cpus; i++)
+		kvfree(pool->cpu_slots[i]);
+	kfree(pool->cpu_slots);
+}
+
+/* initialize object pool and pre-allocate objects */
+int objpool_init(struct objpool_head *pool, int nr_objs, int object_size,
+		gfp_t gfp, void *context, objpool_init_obj_cb objinit,
+		objpool_fini_cb release)
+{
+	int rc, capacity, slot_size;
+
+	/* check input parameters */
+	if (nr_objs <= 0 || nr_objs > OBJPOOL_NR_OBJECT_MAX ||
+	    object_size <= 0 || object_size > OBJPOOL_OBJECT_SIZE_MAX)
+		return -EINVAL;
+
+	/* align up to unsigned long size */
+	object_size = ALIGN(object_size, sizeof(long));
+
+	/* calculate capacity of percpu objpool_slot */
+	capacity = roundup_pow_of_two(nr_objs);
+	if (!capacity)
+		return -EINVAL;
+
+	/* initialize objpool pool */
+	memset(pool, 0, sizeof(struct objpool_head));
+	pool->nr_cpus = nr_cpu_ids;
+	pool->obj_size = object_size;
+	pool->capacity = capacity;
+	pool->gfp = gfp & ~__GFP_ZERO;
+	pool->context = context;
+	pool->release = release;
+	slot_size = pool->nr_cpus * sizeof(struct objpool_slot);
+	pool->cpu_slots = kzalloc(slot_size, pool->gfp);
+	if (!pool->cpu_slots)
+		return -ENOMEM;
+
+	/* initialize per-cpu slots */
+	rc = objpool_init_percpu_slots(pool, nr_objs, context, objinit);
+	if (rc)
+		objpool_fini_percpu_slots(pool);
+	else
+		refcount_set(&pool->ref, pool->nr_objs + 1);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_init);
+
+/* adding object to slot, abort if the slot was already full */
+static inline int
+objpool_try_add_slot(void *obj, struct objpool_head *pool, int cpu)
+{
+	struct objpool_slot *slot = pool->cpu_slots[cpu];
+	uint32_t head, tail;
+
+	/* loading tail and head as a local snapshot, tail first */
+	tail = READ_ONCE(slot->tail);
+
+	do {
+		head = READ_ONCE(slot->head);
+		/* fault caught: something must be wrong */
+		WARN_ON_ONCE(tail - head > pool->nr_objs);
+	} while (!try_cmpxchg_acquire(&slot->tail, &tail, tail + 1));
+
+	/* now the tail position is reserved for the given obj */
+	WRITE_ONCE(slot->entries[tail & slot->mask], obj);
+	/* update sequence to make this obj available for pop() */
+	smp_store_release(&slot->last, tail + 1);
+
+	return 0;
+}
+
+/* reclaim an object to object pool */
+int objpool_push(void *obj, struct objpool_head *pool)
+{
+	unsigned long flags;
+	int rc;
+
+	/* disable local irq to avoid preemption & interruption */
+	raw_local_irq_save(flags);
+	rc = objpool_try_add_slot(obj, pool, raw_smp_processor_id());
+	raw_local_irq_restore(flags);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(objpool_push);
+
+/* try to retrieve object from slot */
+static inline void *objpool_try_get_slot(struct objpool_head *pool, int cpu)
+{
+	struct objpool_slot *slot = pool->cpu_slots[cpu];
+	/* load head snapshot, other cpus may change it */
+	uint32_t head = smp_load_acquire(&slot->head);
+
+	while (head != READ_ONCE(slot->last)) {
+		void *obj;
+
+		/* obj must be retrieved before moving forward head */
+		obj = READ_ONCE(slot->entries[head & slot->mask]);
+
+		/* move head forward to mark it's consumption */
+		if (try_cmpxchg_release(&slot->head, &head, head + 1))
+			return obj;
+	}
+
+	return NULL;
+}
+
+/* allocate an object from object pool */
+void *objpool_pop(struct objpool_head *pool)
+{
+	void *obj = NULL;
+	unsigned long flags;
+	int i, cpu;
+
+	/* disable local irq to avoid preemption & interruption */
+	raw_local_irq_save(flags);
+
+	cpu = raw_smp_processor_id();
+	for (i = 0; i < num_possible_cpus(); i++) {
+		obj = objpool_try_get_slot(pool, cpu);
+		if (obj)
+			break;
+		cpu = cpumask_next_wrap(cpu, cpu_possible_mask, -1, 1);
+	}
+	raw_local_irq_restore(flags);
+
+	return obj;
+}
+EXPORT_SYMBOL_GPL(objpool_pop);
+
+/* release whole objpool forcely */
+void objpool_free(struct objpool_head *pool)
+{
+	if (!pool->cpu_slots)
+		return;
+
+	/* release percpu slots */
+	objpool_fini_percpu_slots(pool);
+
+	/* call user's cleanup callback if provided */
+	if (pool->release)
+		pool->release(pool, pool->context);
+}
+EXPORT_SYMBOL_GPL(objpool_free);
+
+/* drop the allocated object, rather reclaim it to objpool */
+int objpool_drop(void *obj, struct objpool_head *pool)
+{
+	if (!obj || !pool)
+		return -EINVAL;
+
+	if (refcount_dec_and_test(&pool->ref)) {
+		objpool_free(pool);
+		return 0;
+	}
+
+	return -EAGAIN;
+}
+EXPORT_SYMBOL_GPL(objpool_drop);
+
+/* drop unused objects and defref objpool for releasing */
+void objpool_fini(struct objpool_head *pool)
+{
+	int count = 1; /* extra ref for objpool itself */
+
+	/* drop all remained objects from objpool */
+	while (objpool_pop(pool))
+		count++;
+
+	if (refcount_sub_and_test(count, &pool->ref))
+		objpool_free(pool);
+}
+EXPORT_SYMBOL_GPL(objpool_fini);

lib/test_objpool.c

@@ -0,0 +1,690 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Test module for lockless object pool
+ *
+ * Copyright: wuqiang.matt@bytedance.com
+ */
+
+#include <linux/errno.h>
+#include <linux/module.h>
+#include <linux/moduleparam.h>
+#include <linux/completion.h>
+#include <linux/kthread.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/delay.h>
+#include <linux/hrtimer.h>
+#include <linux/objpool.h>
+
+#define OT_NR_MAX_BULK (16)
+
+/* memory usage */
+struct ot_mem_stat {
+	atomic_long_t alloc;
+	atomic_long_t free;
+};
+
+/* object allocation results */
+struct ot_obj_stat {
+	unsigned long nhits;
+	unsigned long nmiss;
+};
+
+/* control & results per testcase */
+struct ot_data {
+	struct rw_semaphore start;
+	struct completion wait;
+	struct completion rcu;
+	atomic_t nthreads ____cacheline_aligned_in_smp;
+	atomic_t stop ____cacheline_aligned_in_smp;
+	struct ot_mem_stat kmalloc;
+	struct ot_mem_stat vmalloc;
+	struct ot_obj_stat objects;
+	u64    duration;
+};
+
+/* testcase */
+struct ot_test {
+	int async; /* synchronous or asynchronous */
+	int mode; /* only mode 0 supported */
+	int objsz; /* object size */
+	int duration; /* ms */
+	int delay; /* ms */
+	int bulk_normal;
+	int bulk_irq;
+	unsigned long hrtimer; /* ms */
+	const char *name;
+	struct ot_data data;
+};
+
+/* per-cpu worker */
+struct ot_item {
+	struct objpool_head *pool; /* pool head */
+	struct ot_test *test; /* test parameters */
+
+	void (*worker)(struct ot_item *item, int irq);
+
+	/* hrtimer control */
+	ktime_t hrtcycle;
+	struct hrtimer hrtimer;
+
+	int bulk[2]; /* for thread and irq */
+	int delay;
+	u32 niters;
+
+	/* summary per thread */
+	struct ot_obj_stat stat[2]; /* thread and irq */
+	u64 duration;
+};
+
+/*
+ * memory leakage checking
+ */
+
+static void *ot_kzalloc(struct ot_test *test, long size)
+{
+	void *ptr = kzalloc(size, GFP_KERNEL);
+
+	if (ptr)
+		atomic_long_add(size, &test->data.kmalloc.alloc);
+	return ptr;
+}
+
+static void ot_kfree(struct ot_test *test, void *ptr, long size)
+{
+	if (!ptr)
+		return;
+	atomic_long_add(size, &test->data.kmalloc.free);
+	kfree(ptr);
+}
+
+static void ot_mem_report(struct ot_test *test)
+{
+	long alloc, free;
+
+	pr_info("memory allocation summary for %s\n", test->name);
+
+	alloc = atomic_long_read(&test->data.kmalloc.alloc);
+	free = atomic_long_read(&test->data.kmalloc.free);
+	pr_info("  kmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+
+	alloc = atomic_long_read(&test->data.vmalloc.alloc);
+	free = atomic_long_read(&test->data.vmalloc.free);
+	pr_info("  vmalloc: %lu - %lu = %lu\n", alloc, free, alloc - free);
+}
+
+/* user object instance */
+struct ot_node {
+	void *owner;
+	unsigned long data;
+	unsigned long refs;
+	unsigned long payload[32];
+};
+
+/* user objpool manager */
+struct ot_context {
+	struct objpool_head pool; /* objpool head */
+	struct ot_test *test; /* test parameters */
+	void *ptr; /* user pool buffer */
+	unsigned long size; /* buffer size */
+	struct rcu_head rcu;
+};
+
+static DEFINE_PER_CPU(struct ot_item, ot_pcup_items);
+
+static int ot_init_data(struct ot_data *data)
+{
+	memset(data, 0, sizeof(*data));
+	init_rwsem(&data->start);
+	init_completion(&data->wait);
+	init_completion(&data->rcu);
+	atomic_set(&data->nthreads, 1);
+
+	return 0;
+}
+
+static int ot_init_node(void *nod, void *context)
+{
+	struct ot_context *sop = context;
+	struct ot_node *on = nod;
+
+	on->owner = &sop->pool;
+	return 0;
+}
+
+static enum hrtimer_restart ot_hrtimer_handler(struct hrtimer *hrt)
+{
+	struct ot_item *item = container_of(hrt, struct ot_item, hrtimer);
+	struct ot_test *test = item->test;
+
+	if (atomic_read_acquire(&test->data.stop))
+		return HRTIMER_NORESTART;
+
+	/* do bulk-testings for objects pop/push */
+	item->worker(item, 1);
+
+	hrtimer_forward(hrt, hrt->base->get_time(), item->hrtcycle);
+	return HRTIMER_RESTART;
+}
+
+static void ot_start_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_start(&item->hrtimer, item->hrtcycle, HRTIMER_MODE_REL);
+}
+
+static void ot_stop_hrtimer(struct ot_item *item)
+{
+	if (!item->test->hrtimer)
+		return;
+	hrtimer_cancel(&item->hrtimer);
+}
+
+static int ot_init_hrtimer(struct ot_item *item, unsigned long hrtimer)
+{
+	struct hrtimer *hrt = &item->hrtimer;
+
+	if (!hrtimer)
+		return -ENOENT;
+
+	item->hrtcycle = ktime_set(0, hrtimer * 1000000UL);
+	hrtimer_init(hrt, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrt->function = ot_hrtimer_handler;
+	return 0;
+}
+
+static int ot_init_cpu_item(struct ot_item *item,
+			struct ot_test *test,
+			struct objpool_head *pool,
+			void (*worker)(struct ot_item *, int))
+{
+	memset(item, 0, sizeof(*item));
+	item->pool = pool;
+	item->test = test;
+	item->worker = worker;
+
+	item->bulk[0] = test->bulk_normal;
+	item->bulk[1] = test->bulk_irq;
+	item->delay = test->delay;
+
+	/* initialize hrtimer */
+	ot_init_hrtimer(item, item->test->hrtimer);
+	return 0;
+}
+
+static int ot_thread_worker(void *arg)
+{
+	struct ot_item *item = arg;
+	struct ot_test *test = item->test;
+	ktime_t start;
+
+	atomic_inc(&test->data.nthreads);
+	down_read(&test->data.start);
+	up_read(&test->data.start);
+	start = ktime_get();
+	ot_start_hrtimer(item);
+	do {
+		if (atomic_read_acquire(&test->data.stop))
+			break;
+		/* do bulk-testings for objects pop/push */
+		item->worker(item, 0);
+	} while (!kthread_should_stop());
+	ot_stop_hrtimer(item);
+	item->duration = (u64) ktime_us_delta(ktime_get(), start);
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	return 0;
+}
+
+static void ot_perf_report(struct ot_test *test, u64 duration)
+{
+	struct ot_obj_stat total, normal = {0}, irq = {0};
+	int cpu, nthreads = 0;
+
+	pr_info("\n");
+	pr_info("Testing summary for %s\n", test->name);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		if (!item->duration)
+			continue;
+		normal.nhits += item->stat[0].nhits;
+		normal.nmiss += item->stat[0].nmiss;
+		irq.nhits += item->stat[1].nhits;
+		irq.nmiss += item->stat[1].nmiss;
+		pr_info("CPU: %d  duration: %lluus\n", cpu, item->duration);
+		pr_info("\tthread:\t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits, item->stat[0].nmiss);
+		pr_info("\tirq:   \t%16lu hits \t%16lu miss\n",
+			item->stat[1].nhits, item->stat[1].nmiss);
+		pr_info("\ttotal: \t%16lu hits \t%16lu miss\n",
+			item->stat[0].nhits + item->stat[1].nhits,
+			item->stat[0].nmiss + item->stat[1].nmiss);
+		nthreads++;
+	}
+
+	total.nhits = normal.nhits + irq.nhits;
+	total.nmiss = normal.nmiss + irq.nmiss;
+
+	pr_info("ALL: \tnthreads: %d  duration: %lluus\n", nthreads, duration);
+	pr_info("SUM: \t%16lu hits \t%16lu miss\n",
+		total.nhits, total.nmiss);
+
+	test->data.objects = total;
+	test->data.duration = duration;
+}
+
+/*
+ * synchronous test cases for objpool manipulation
+ */
+
+/* objpool manipulation for synchronous mode (percpu objpool) */
+static struct ot_context *ot_init_sync_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz,
+			 gfp, sop, ot_init_node, NULL)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+static void ot_fini_sync(struct ot_context *sop)
+{
+	objpool_fini(&sop->pool);
+	ot_kfree(sop->test, sop, sizeof(*sop));
+}
+
+struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_sync_ops[] = {
+	{.init = ot_init_sync_m0, .fini = ot_fini_sync},
+};
+
+/*
+ * synchronous test cases: performance mode
+ */
+
+static void ot_bulk_sync(struct ot_item *item, int irq)
+{
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq && (item->delay || !(++(item->niters) & 0x7FFF)))
+		msleep(item->delay);
+
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+		if (on) {
+			on->refs++;
+			objpool_push(on, item->pool);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+}
+
+static int ot_start_sync(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_sync_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_sync);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_create_on_node(ot_thread_worker, item,
+				cpu_to_node(cpu), "ot_worker_%d", cpu);
+		if (IS_ERR(work)) {
+			pr_err("failed to create thread for cpu %d\n", cpu);
+		} else {
+			kthread_bind(work, cpu);
+			wake_up_process(work);
+		}
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	// sched_set_fifo_low(current);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* cleanup objpool */
+	g_ot_sync_ops[test->mode].fini(sop);
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * asynchronous test cases: pool lifecycle controlled by refcount
+ */
+
+static void ot_fini_async_rcu(struct rcu_head *rcu)
+{
+	struct ot_context *sop = container_of(rcu, struct ot_context, rcu);
+	struct ot_test *test = sop->test;
+
+	/* here all cpus are aware of the stop event: test->data.stop = 1 */
+	WARN_ON(!atomic_read_acquire(&test->data.stop));
+
+	objpool_fini(&sop->pool);
+	complete(&test->data.rcu);
+}
+
+static void ot_fini_async(struct ot_context *sop)
+{
+	/* make sure the stop event is acknowledged by all cores */
+	call_rcu(&sop->rcu, ot_fini_async_rcu);
+}
+
+static int ot_objpool_release(struct objpool_head *head, void *context)
+{
+	struct ot_context *sop = context;
+
+	WARN_ON(!head || !sop || head != &sop->pool);
+
+	/* do context cleaning if needed */
+	if (sop)
+		ot_kfree(sop->test, sop, sizeof(*sop));
+
+	return 0;
+}
+
+static struct ot_context *ot_init_async_m0(struct ot_test *test)
+{
+	struct ot_context *sop = NULL;
+	int max = num_possible_cpus() << 3;
+	gfp_t gfp = GFP_KERNEL;
+
+	sop = (struct ot_context *)ot_kzalloc(test, sizeof(*sop));
+	if (!sop)
+		return NULL;
+	sop->test = test;
+	if (test->objsz < 512)
+		gfp = GFP_ATOMIC;
+
+	if (objpool_init(&sop->pool, max, test->objsz, gfp, sop,
+			 ot_init_node, ot_objpool_release)) {
+		ot_kfree(test, sop, sizeof(*sop));
+		return NULL;
+	}
+	WARN_ON(max != sop->pool.nr_objs);
+
+	return sop;
+}
+
+struct {
+	struct ot_context * (*init)(struct ot_test *oc);
+	void (*fini)(struct ot_context *sop);
+} g_ot_async_ops[] = {
+	{.init = ot_init_async_m0, .fini = ot_fini_async},
+};
+
+static void ot_nod_recycle(struct ot_node *on, struct objpool_head *pool,
+			int release)
+{
+	struct ot_context *sop;
+
+	on->refs++;
+
+	if (!release) {
+		/* push object back to opjpool for reuse */
+		objpool_push(on, pool);
+		return;
+	}
+
+	sop = container_of(pool, struct ot_context, pool);
+	WARN_ON(sop != pool->context);
+
+	/* unref objpool with nod removed forever */
+	objpool_drop(on, pool);
+}
+
+static void ot_bulk_async(struct ot_item *item, int irq)
+{
+	struct ot_test *test = item->test;
+	struct ot_node *nods[OT_NR_MAX_BULK];
+	int i, stop;
+
+	for (i = 0; i < item->bulk[irq]; i++)
+		nods[i] = objpool_pop(item->pool);
+
+	if (!irq) {
+		if (item->delay || !(++(item->niters) & 0x7FFF))
+			msleep(item->delay);
+		get_cpu();
+	}
+
+	stop = atomic_read_acquire(&test->data.stop);
+
+	/* drop all objects and deref objpool */
+	while (i-- > 0) {
+		struct ot_node *on = nods[i];
+
+		if (on) {
+			on->refs++;
+			ot_nod_recycle(on, item->pool, stop);
+			item->stat[irq].nhits++;
+		} else {
+			item->stat[irq].nmiss++;
+		}
+	}
+
+	if (!irq)
+		put_cpu();
+}
+
+static int ot_start_async(struct ot_test *test)
+{
+	struct ot_context *sop;
+	ktime_t start;
+	u64 duration;
+	unsigned long timeout;
+	int cpu;
+
+	/* initialize objpool for syncrhonous testcase */
+	sop = g_ot_async_ops[test->mode].init(test);
+	if (!sop)
+		return -ENOMEM;
+
+	/* grab rwsem to block testing threads */
+	down_write(&test->data.start);
+
+	for_each_possible_cpu(cpu) {
+		struct ot_item *item = per_cpu_ptr(&ot_pcup_items, cpu);
+		struct task_struct *work;
+
+		ot_init_cpu_item(item, test, &sop->pool, ot_bulk_async);
+
+		/* skip offline cpus */
+		if (!cpu_online(cpu))
+			continue;
+
+		work = kthread_create_on_node(ot_thread_worker, item,
+				cpu_to_node(cpu), "ot_worker_%d", cpu);
+		if (IS_ERR(work)) {
+			pr_err("failed to create thread for cpu %d\n", cpu);
+		} else {
+			kthread_bind(work, cpu);
+			wake_up_process(work);
+		}
+	}
+
+	/* wait a while to make sure all threads waiting at start line */
+	msleep(20);
+
+	/* in case no threads were created: memory insufficient ? */
+	if (atomic_dec_and_test(&test->data.nthreads))
+		complete(&test->data.wait);
+
+	/* start objpool testing threads */
+	start = ktime_get();
+	up_write(&test->data.start);
+
+	/* yeild cpu to worker threads for duration ms */
+	timeout = msecs_to_jiffies(test->duration);
+	schedule_timeout_interruptible(timeout);
+
+	/* tell workers threads to quit */
+	atomic_set_release(&test->data.stop, 1);
+
+	/* do async-finalization */
+	g_ot_async_ops[test->mode].fini(sop);
+
+	/* wait all workers threads finish and quit */
+	wait_for_completion(&test->data.wait);
+	duration = (u64) ktime_us_delta(ktime_get(), start);
+
+	/* assure rcu callback is triggered */
+	wait_for_completion(&test->data.rcu);
+
+	/*
+	 * now we are sure that objpool is finalized either
+	 * by rcu callback or by worker threads
+	 */
+
+	/* report testing summary and performance results */
+	ot_perf_report(test, duration);
+
+	/* report memory allocation summary */
+	ot_mem_report(test);
+
+	return 0;
+}
+
+/*
+ * predefined testing cases:
+ *   synchronous case / overrun case / async case
+ *
+ * async: synchronous or asynchronous testing
+ * mode: only mode 0 supported
+ * objsz: object size
+ * duration: int, total test time in ms
+ * delay: int, delay (in ms) between each iteration
+ * bulk_normal: int, repeat times for thread worker
+ * bulk_irq: int, repeat times for irq consumer
+ * hrtimer: unsigned long, hrtimer intervnal in ms
+ * name: char *, tag for current test ot_item
+ */
+
+#define NODE_COMPACT sizeof(struct ot_node)
+#define NODE_VMALLOC (512)
+
+struct ot_test g_testcases[] = {
+
+	/* sync & normal */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  0,  0, "sync: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  0,  0, "sync: percpu objpool from vmalloc"},
+
+	/* sync & hrtimer */
+	{0, 0, NODE_COMPACT, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0,  1,  1,  4, "sync & hrtimer: percpu objpool from vmalloc"},
+
+	/* sync & overrun */
+	{0, 0, NODE_COMPACT, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool"},
+	{0, 0, NODE_VMALLOC, 1000, 0, 16,  0,  0, "sync overrun: percpu objpool from vmalloc"},
+
+	/* async mode */
+	{1, 0, NODE_COMPACT, 1000, 100,  1,  0,  0, "async: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 100,  1,  0,  0, "async: percpu objpool from vmalloc"},
+
+	/* async + hrtimer mode */
+	{1, 0, NODE_COMPACT, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool"},
+	{1, 0, NODE_VMALLOC, 1000, 0,  4,  4,  4, "async & hrtimer: percpu objpool from vmalloc"},
+};
+
+static int __init ot_mod_init(void)
+{
+	int i;
+
+	/* perform testings */
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		ot_init_data(&g_testcases[i].data);
+		if (g_testcases[i].async)
+			ot_start_async(&g_testcases[i]);
+		else
+			ot_start_sync(&g_testcases[i]);
+	}
+
+	/* show tests summary */
+	pr_info("\n");
+	pr_info("Summary of testcases:\n");
+	for (i = 0; i < ARRAY_SIZE(g_testcases); i++) {
+		pr_info("    duration: %lluus \thits: %10lu \tmiss: %10lu \t%s\n",
+			g_testcases[i].data.duration, g_testcases[i].data.objects.nhits,
+			g_testcases[i].data.objects.nmiss, g_testcases[i].name);
+	}
+
+	return -EAGAIN;
+}
+
+static void __exit ot_mod_exit(void)
+{
+}
+
+module_init(ot_mod_init);
+module_exit(ot_mod_exit);
+
+MODULE_LICENSE("GPL");