[PATCH v7] io_uring: Statistics of the true utilization of sq threads.

[Xiaobing Li]

Count the running time and actual IO processing time of the sqpoll
thread, and output the statistical data to fdinfo.

Variable description:
"work_time" in the code represents the sum of the jiffies of the sq
thread actually processing IO, that is, how many milliseconds it
actually takes to process IO. "total_time" represents the total time
that the sq thread has elapsed from the beginning of the loop to the
current time point, that is, how many milliseconds it has spent in
total.

The test tool is fio, and its parameters are as follows:
[global]
ioengine=io_uring
direct=1
group_reporting
bs=128k
norandommap=1
randrepeat=0
refill_buffers
ramp_time=30s
time_based
runtime=1m
clocksource=clock_gettime
overwrite=1
log_avg_msec=1000
numjobs=1

[disk0]
filename=/dev/nvme0n1
rw=read
iodepth=16
hipri
sqthread_poll=1

---
The test results are as follows:
Every 2.0s: cat /proc/9230/fdinfo/6 | grep -E Sq
SqMask: 0x3
SqHead: 3197153
SqTail: 3197153
CachedSqHead:   3197153
SqThread:       9231
SqThreadCpu:    11
SqTotalTime:    18099614us
SqWorkTime:     16748316us

---
The test results corresponding to different iodepths are as follows:
|-----------|-------|-------|-------|------|-------|
|   iodepth |   1   |   4   |   8   |  16  |  64   |
|-----------|-------|-------|-------|------|-------|
|utilization| 2.9%  | 8.8%  | 10.9% | 92.9%| 84.4% |
|-----------|-------|-------|-------|------|-------|
|    idle   | 97.1% | 91.2% | 89.1% | 7.1% | 15.6% |
|-----------|-------|-------|-------|------|-------|

changes：
v7:
 - Get the total time of the sqpoll thread through getrusage
 - The working time of the sqpoll thread is obtained through ktime_get()

v6:
 - Replace the percentages in the fdinfo output with the actual running
time and the time actually processing IO

v5：
 - list the changes in each iteration.

v4：
 - Resubmit the patch based on removing sq->lock

v3：
 - output actual working time as a percentage of total time
 - detailed description of the meaning of each variable
 - added test results

v2：
 - output the total statistical time and work time to fdinfo

v1：
 - initial version
 - Statistics of total time and work time

Signed-off-by: Xiaobing Li <xiaobing.li@xxxxxxxxxxx>
---
 io_uring/fdinfo.c | 8 ++++++++
 io_uring/sqpoll.c | 7 +++++++
 io_uring/sqpoll.h | 1 +
 3 files changed, 16 insertions(+)

diff --git a/io_uring/fdinfo.c b/io_uring/fdinfo.c
index 976e9500f651..24a7452ed98e 100644
--- a/io_uring/fdinfo.c
+++ b/io_uring/fdinfo.c
@@ -64,6 +64,7 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
 	unsigned int sq_shift = 0;
 	unsigned int sq_entries, cq_entries;
 	int sq_pid = -1, sq_cpu = -1;
+	long long sq_total_time = 0, sq_work_time = 0;
 	bool has_lock;
 	unsigned int i;
 
@@ -147,10 +148,17 @@ __cold void io_uring_show_fdinfo(struct seq_file *m, struct file *f)
 
 		sq_pid = sq->task_pid;
 		sq_cpu = sq->sq_cpu;
+		struct rusage r;
+
+		getrusage(sq->thread, RUSAGE_SELF, &r);
+		sq_total_time = r.ru_stime.tv_sec * 1000000 + r.ru_stime.tv_usec;
+		sq_work_time = sq->work_time;
 	}
 
 	seq_printf(m, "SqThread:\t%d\n", sq_pid);
 	seq_printf(m, "SqThreadCpu:\t%d\n", sq_cpu);
+	seq_printf(m, "SqTotalTime:\t%lldus\n", sq_total_time);
+	seq_printf(m, "SqWorkTime:\t%lldus\n", sq_work_time);
 	seq_printf(m, "UserFiles:\t%u\n", ctx->nr_user_files);
 	for (i = 0; has_lock && i < ctx->nr_user_files; i++) {
 		struct file *f = io_file_from_index(&ctx->file_table, i);
diff --git a/io_uring/sqpoll.c b/io_uring/sqpoll.c
index 65b5dbe3c850..f3e9fda72400 100644
--- a/io_uring/sqpoll.c
+++ b/io_uring/sqpoll.c
@@ -251,6 +251,9 @@ static int io_sq_thread(void *data)
 		}
 
 		cap_entries = !list_is_singular(&sqd->ctx_list);
+		ktime_t start, diff;
+
+		start = ktime_get();
 		list_for_each_entry(ctx, &sqd->ctx_list, sqd_list) {
 			int ret = __io_sq_thread(ctx, cap_entries);
 
@@ -260,6 +263,10 @@ static int io_sq_thread(void *data)
 		if (io_run_task_work())
 			sqt_spin = true;
 
+		diff = ktime_sub(ktime_get(), start);
+		if (sqt_spin == true)
+			sqd->work_time += ktime_to_us(diff);
+
 		if (sqt_spin || !time_after(jiffies, timeout)) {
 			if (sqt_spin)
 				timeout = jiffies + sqd->sq_thread_idle;
diff --git a/io_uring/sqpoll.h b/io_uring/sqpoll.h
index 8df37e8c9149..c14c00240443 100644
--- a/io_uring/sqpoll.h
+++ b/io_uring/sqpoll.h
@@ -16,6 +16,7 @@ struct io_sq_data {
 	pid_t			task_pid;
 	pid_t			task_tgid;
 
+	long long			work_time;
 	unsigned long		state;
 	struct completion	exited;
 };
-- 
2.34.1