[PATCH V2 5/5] selftests: ublk: make ublk_thread thread-local variable

[Ming Lei <ming.lei@redhat.com>]

Refactor ublk_thread to be a thread-local variable instead of storing
it in ublk_dev:

- Remove pthread_t thread field from struct ublk_thread and move it to
  struct ublk_thread_info

- Remove struct ublk_thread array from struct ublk_dev, reducing memory
  footprint

- Define struct ublk_thread as local variable in __ublk_io_handler_fn()
  instead of accessing it from dev->threads[]

- Extract main IO handling logic into __ublk_io_handler_fn() which is
  marked as noinline

- Move CPU affinity setup to ublk_io_handler_fn() before calling
  __ublk_io_handler_fn()

- Update ublk_thread_set_sched_affinity() to take struct ublk_thread_info *
  instead of struct ublk_thread *, and use pthread_setaffinity_np()
  instead of sched_setaffinity()

- Reorder struct ublk_thread fields to group related state together

This change makes each thread's ublk_thread structure truly local to
the thread, improving cache locality and reducing memory usage.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 tools/testing/selftests/ublk/kublk.c | 76 +++++++++++++++-------------
 tools/testing/selftests/ublk/kublk.h |  9 ++--
 2 files changed, 45 insertions(+), 40 deletions(-)

diff --git a/tools/testing/selftests/ublk/kublk.c b/tools/testing/selftests/ublk/kublk.c
index 062537ab8976..f8fa102a627f 100644
--- a/tools/testing/selftests/ublk/kublk.c
+++ b/tools/testing/selftests/ublk/kublk.c
@@ -836,62 +836,70 @@ static int ublk_process_io(struct ublk_thread *t)
 	return reapped;
 }
 
-static void ublk_thread_set_sched_affinity(const struct ublk_thread *t,
-		cpu_set_t *cpuset)
-{
-	if (pthread_setaffinity_np(pthread_self(), sizeof(*cpuset), cpuset) < 0)
-		ublk_err("ublk dev %u thread %u set affinity failed",
-				t->dev->dev_info.dev_id, t->idx);
-}
-
 struct ublk_thread_info {
 	struct ublk_dev 	*dev;
+	pthread_t		thread;
 	unsigned		idx;
 	sem_t 			*ready;
 	cpu_set_t 		*affinity;
 	unsigned long long	extra_flags;
 };
 
-static void *ublk_io_handler_fn(void *data)
+static void ublk_thread_set_sched_affinity(const struct ublk_thread_info *info)
 {
-	struct ublk_thread_info *info = data;
-	struct ublk_thread *t = &info->dev->threads[info->idx];
+	if (pthread_setaffinity_np(pthread_self(), sizeof(*info->affinity), info->affinity) < 0)
+		ublk_err("ublk dev %u thread %u set affinity failed",
+				info->dev->dev_info.dev_id, info->idx);
+}
+
+static __attribute__((noinline)) int __ublk_io_handler_fn(struct ublk_thread_info *info)
+{
+	struct ublk_thread t = {
+		.dev = info->dev,
+		.idx = info->idx,
+	};
 	int dev_id = info->dev->dev_info.dev_id;
 	int ret;
 
-	t->dev = info->dev;
-	t->idx = info->idx;
-
-	/*
-	 * IO perf is sensitive with queue pthread affinity on NUMA machine
-	 *
-	 * Set sched_affinity at beginning, so following allocated memory/pages
-	 * could be CPU/NUMA aware.
-	 */
-	if (info->affinity)
-		ublk_thread_set_sched_affinity(t, info->affinity);
-
-	ret = ublk_thread_init(t, info->extra_flags);
+	ret = ublk_thread_init(&t, info->extra_flags);
 	if (ret) {
 		ublk_err("ublk dev %d thread %u init failed\n",
-				dev_id, t->idx);
-		return NULL;
+				dev_id, t.idx);
+		return ret;
 	}
 	sem_post(info->ready);
 
 	ublk_dbg(UBLK_DBG_THREAD, "tid %d: ublk dev %d thread %u started\n",
-			gettid(), dev_id, t->idx);
+			gettid(), dev_id, t.idx);
 
 	/* submit all io commands to ublk driver */
-	ublk_submit_fetch_commands(t);
+	ublk_submit_fetch_commands(&t);
 	do {
-		if (ublk_process_io(t) < 0)
+		if (ublk_process_io(&t) < 0)
 			break;
 	} while (1);
 
 	ublk_dbg(UBLK_DBG_THREAD, "tid %d: ublk dev %d thread %d exiting\n",
-		 gettid(), dev_id, t->idx);
-	ublk_thread_deinit(t);
+		 gettid(), dev_id, t.idx);
+	ublk_thread_deinit(&t);
+	return 0;
+}
+
+static void *ublk_io_handler_fn(void *data)
+{
+	struct ublk_thread_info *info = data;
+
+	/*
+	 * IO perf is sensitive with queue pthread affinity on NUMA machine
+	 *
+	 * Set sched_affinity at beginning, so following allocated memory/pages
+	 * could be CPU/NUMA aware.
+	 */
+	if (info->affinity)
+		ublk_thread_set_sched_affinity(info);
+
+	__ublk_io_handler_fn(info);
+
 	return NULL;
 }
 
@@ -989,14 +997,13 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev)
 		 */
 		if (dev->nthreads == dinfo->nr_hw_queues)
 			tinfo[i].affinity = &affinity_buf[i];
-		pthread_create(&dev->threads[i].thread, NULL,
+		pthread_create(&tinfo[i].thread, NULL,
 				ublk_io_handler_fn,
 				&tinfo[i]);
 	}
 
 	for (i = 0; i < dev->nthreads; i++)
 		sem_wait(&ready);
-	free(tinfo);
 	free(affinity_buf);
 
 	/* everything is fine now, start us */
@@ -1019,7 +1026,8 @@ static int ublk_start_daemon(const struct dev_ctx *ctx, struct ublk_dev *dev)
 
 	/* wait until we are terminated */
 	for (i = 0; i < dev->nthreads; i++)
-		pthread_join(dev->threads[i].thread, &thread_ret);
+		pthread_join(tinfo[i].thread, &thread_ret);
+	free(tinfo);
  fail:
 	for (i = 0; i < dinfo->nr_hw_queues; i++)
 		ublk_queue_deinit(&dev->q[i]);
diff --git a/tools/testing/selftests/ublk/kublk.h b/tools/testing/selftests/ublk/kublk.h
index 5e55484fb0aa..fe42705c6d42 100644
--- a/tools/testing/selftests/ublk/kublk.h
+++ b/tools/testing/selftests/ublk/kublk.h
@@ -175,23 +175,20 @@ struct ublk_queue {
 
 struct ublk_thread {
 	struct ublk_dev *dev;
-	struct io_uring ring;
-	unsigned int cmd_inflight;
-	unsigned int io_inflight;
-
-	pthread_t thread;
 	unsigned idx;
 
 #define UBLKS_T_STOPPING	(1U << 0)
 #define UBLKS_T_IDLE	(1U << 1)
 	unsigned state;
+	unsigned int cmd_inflight;
+	unsigned int io_inflight;
+	struct io_uring ring;
 };
 
 struct ublk_dev {
 	struct ublk_tgt tgt;
 	struct ublksrv_ctrl_dev_info  dev_info;
 	struct ublk_queue q[UBLK_MAX_QUEUES];
-	struct ublk_thread threads[UBLK_MAX_THREADS];
 	unsigned nthreads;
 	unsigned per_io_tasks;
 
-- 
2.47.0