[PATCH v2 1/4] PM: freezer: Add retry count statistics for freeze pass iterations

[Zihuan Zhang]

Freezer retry loops during suspend are often triggered by tasks entering
D-state (TASK_UNINTERRUPTIBLE), which cannot be frozen.  This patch adds
a simple retry counter to freeze_processes() to help quantify how many
attempts were required before all tasks entered the frozen state. This
is useful for performance tuning and debugging unpredictable suspend
delays.

A new dmesg log is added for visibility:

freeze round: xx, tasks to freeze: xx

This message allows users to correlate freeze instability with system
state.

Signed-off-by: Zihuan Zhang <zhangzihuan@xxxxxxxxxx>
---
 kernel/power/process.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/kernel/power/process.c b/kernel/power/process.c
index dc0dfc349f22..87616ca710ac 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -32,6 +32,7 @@ static int try_to_freeze_tasks(bool user_only)
 	struct task_struct *g, *p;
 	unsigned long end_time;
 	unsigned int todo;
+	unsigned int retry = 0;
 	bool wq_busy = false;
 	ktime_t start, end, elapsed;
 	unsigned int elapsed_msecs;
@@ -63,6 +64,8 @@ static int try_to_freeze_tasks(bool user_only)
 			todo += wq_busy;
 		}
 
+		pm_pr_dbg("freeze round: %d, task to freeze: %d\n", retry, todo);
+
 		if (!todo || time_after(jiffies, end_time))
 			break;
 
@@ -79,6 +82,7 @@ static int try_to_freeze_tasks(bool user_only)
 		usleep_range(sleep_usecs / 2, sleep_usecs);
 		if (sleep_usecs < 8 * USEC_PER_MSEC)
 			sleep_usecs *= 2;
+		retry++;
 	}
 
 	end = ktime_get_boottime();
-- 
2.25.1