uring_fn
+   23.26%  iou-sqp-819  [kernel.kallsyms]  [k] io_sq_thread
+   10.14%  iou-sqp-819  [kernel.kallsyms]  [k] io_sq_tw
+    6.52%  iou-sqp-819  [kernel.kallsyms]  [k] tctx_task_work_run
+    4.82%  iou-sqp-819  [kernel.kallsyms]  [k] nvme_submit_cmds.part.0
+    2.91%  iou-sqp-819  [kernel.kallsyms]  [k] io_submit_sqes
[...]
     0.02%  iou-sqp-819  [kernel.kallsyms]  [k] cputime_adjust

where it's spending the cycles on things that actually matter.

Reported-by: Fengnan Chang <changfengnan@bytedance.com>
Cc: stable@vger.kernel.org
Fixes: 3fcb9d17206e ("io_uring/sqpoll: statistics of the true utilization of sq threads")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/sqpoll.c | 43 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 32 insertions(+), 11 deletions(-)

diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 2b816fdb9866..e22f072c7d5f 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -170,6 +170,11 @@ static inline bool io_sqd_events_pending(struct io_sq_data *sqd)
 	return READ_ONCE(sqd->state);
 }
 
+struct io_sq_time {
+	bool started;
+	u64 usec;
+};
+
 u64 io_sq_cpu_usec(struct task_struct *tsk)
 {
 	u64 utime, stime;
@@ -179,12 +184,24 @@ u64 io_sq_cpu_usec(struct task_struct *tsk)
 	return stime;
 }
 
-static void io_sq_update_worktime(struct io_sq_data *sqd, u64 usec)
+static void io_sq_update_worktime(struct io_sq_data *sqd, struct io_sq_time *ist)
+{
+	if (!ist->started)
+		return;
+	ist->started = false;
+	sqd->work_time += io_sq_cpu_usec(current) - ist->usec;
+}
+
+static void io_sq_start_worktime(struct io_sq_time *ist)
 {
-	sqd->work_time += io_sq_cpu_usec(current) - usec;
+	if (ist->started)
+		return;
+	ist->started = true;
+	ist->usec = io_sq_cpu_usec(current);
 }
 
-static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
+static int __io_sq_thread(struct io_ring_ctx *ctx, struct io_sq_data *sqd,
+			  bool cap_entries, struct io_sq_time *ist)
 {
 	unsigned int to_submit;
 	int ret = 0;
@@ -197,6 +214,8 @@ static int __io_sq_thread(struct io_ring_ctx *ctx, bool cap_entries)
 	if (to_submit || !wq_list_empty(&ctx->iopoll_list)) {
 		const struct cred *creds = NULL;
 
+		io_sq_start_worktime(ist);
+
 		if (ctx->sq_creds != current_cred())
 			creds = override_creds(ctx->sq_creds);
 
@@ -278,7 +297,6 @@ static int io_sq_thread(void *data)
 	unsigned long timeout = 0;
 	char buf[TASK_COMM_LEN] = {};
 	DEFINE_WAIT(wait);
-	u64 start;
 
 	/* offload context creation failed, just exit */
 	if (!current->io_uring) {
@@ -313,6 +331,7 @@ static int io_sq_thread(void *data)
 	mutex_lock(&sqd->lock);
 	while (1) {
 		bool cap_entries, sqt_spin = false;
+		struct io_sq_time ist = { };
 
 		if (io_sqd_events_pending(sqd) || signal_pending(current)) {
 			if (io_sqd_handle_event(sqd))
@@ -321,9 +340,8 @@ static int io_sq_thread(void *data)
 		}
 
 		cap_entries = !list_is_singular(&sqd->ctx_list);
-		start = io_sq_cpu_usec(current);
 		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
-			int ret = __io_sq_thread(ctx, cap_entries);
+			int ret = __io_sq_thread(ctx, sqd, cap_entries, &ist);
 
 			if (!sqt_spin && (ret > 0 || !wq_list_empty(&ctx->iopoll_list)))
 				sqt_spin = true;
@@ -331,15 +349,18 @@ static int io_sq_thread(void *data)
 		if (io_sq_tw(&retry_list, IORING_TW_CAP_ENTRIES_VALUE))
 			sqt_spin = true;
 
-		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list)
-			if (io_napi(ctx))
+		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
+			if (io_napi(ctx)) {
+				io_sq_start_worktime(&ist);
 				io_napi_sqpoll_busy_poll(ctx);
+			}
+		}
+
+		io_sq_update_worktime(sqd, &ist);
 
 		if (sqt_spin || !time_after(jiffies, timeout)) {
-			if (sqt_spin) {
-				io_sq_update_worktime(sqd, start);
+			if (sqt_spin)
 				timeout = jiffies + sqd->sq_thread_idle;
-			}
 			if (unlikely(need_resched())) {
 				mutex_unlock(&sqd->lock);
 				cond_resched();
-- 
2.51.0[PATCH 2/2] io_uring/sqpoll: be smarter on when to update the stime usageJens Axboe <axboe@kernel.dk> undefinedio-uring@vger.kernel.org undefined undefined undefined undefined undefined undefined