[PATCH v5] PM / sleep: measure the time of filesystem syncing

[Harry Pan]

This patch gives the reader an intuitive metric of the time cost by
the kernel issuing a filesystem sync during system sleep; although
developer can guess by the timestamp of next log or enable the ftrace
power event for manual calculation, this manner is easier to read and
benefits the automatic script.

v2: simplify the variables, apply the simplest form of ktime API.
v3: reduce conditional compilation, rectify profiling in better syntax
v4: avoid interposition, profile on hibernation, rectify printk format
v5: introduce sync helper shared by suspend, hibernate, and snapshot

Signed-off-by: Harry Pan <harry.pan@xxxxxxxxx>
---
 include/linux/suspend.h  |  3 +++
 kernel/power/hibernate.c |  4 +---
 kernel/power/main.c      | 15 +++++++++++++++
 kernel/power/suspend.c   | 13 +++++--------
 kernel/power/user.c      |  4 +---
 5 files changed, 25 insertions(+), 14 deletions(-)

diff --git a/include/linux/suspend.h b/include/linux/suspend.h
index 3f529ad9a9d2..6b3ea9ea6a9e 100644
--- a/include/linux/suspend.h
+++ b/include/linux/suspend.h
@@ -425,6 +425,7 @@ void restore_processor_state(void);
 /* kernel/power/main.c */
 extern int register_pm_notifier(struct notifier_block *nb);
 extern int unregister_pm_notifier(struct notifier_block *nb);
+extern void ksys_sync_helper(void);
 
 #define pm_notifier(fn, pri) {				\
 	static struct notifier_block fn##_nb =			\
@@ -462,6 +463,8 @@ static inline int unregister_pm_notifier(struct notifier_block *nb)
 	return 0;
 }
 
+static inline void ksys_sync_helper(void) {}
+
 #define pm_notifier(fn, pri)	do { (void)(fn); } while (0)
 
 static inline bool pm_wakeup_pending(void) { return false; }
diff --git a/kernel/power/hibernate.c b/kernel/power/hibernate.c
index abef759de7c8..895f43a5f10c 100644
--- a/kernel/power/hibernate.c
+++ b/kernel/power/hibernate.c
@@ -709,9 +709,7 @@ int hibernate(void)
 		goto Exit;
 	}
 
-	pr_info("Syncing filesystems ... \n");
-	ksys_sync();
-	pr_info("done.\n");
+	ksys_sync_helper();
 
 	error = freeze_processes();
 	if (error)
diff --git a/kernel/power/main.c b/kernel/power/main.c
index 35b50823d83b..a08dcc743f31 100644
--- a/kernel/power/main.c
+++ b/kernel/power/main.c
@@ -16,6 +16,7 @@
 #include <linux/debugfs.h>
 #include <linux/seq_file.h>
 #include <linux/suspend.h>
+#include <linux/syscalls.h>
 
 #include "power.h"
 
@@ -51,6 +52,20 @@ void unlock_system_sleep(void)
 }
 EXPORT_SYMBOL_GPL(unlock_system_sleep);
 
+void ksys_sync_helper(void)
+{
+	ktime_t start;
+	s64 elapsed_msecs;
+
+	start = ktime_get();
+	ksys_sync();
+	elapsed_msecs = ktime_to_ms(ktime_sub(ktime_get(), start));
+	pr_info("Filesystems sync: %lld.%03lld seconds\n",
+		elapsed_msecs / MSEC_PER_SEC,
+		elapsed_msecs % MSEC_PER_SEC);
+}
+EXPORT_SYMBOL_GPL(ksys_sync_helper);
+
 /* Routines for PM-transition notifications */
 
 static BLOCKING_NOTIFIER_HEAD(pm_chain_head);
diff --git a/kernel/power/suspend.c b/kernel/power/suspend.c
index 0bd595a0b610..e39059dea38b 100644
--- a/kernel/power/suspend.c
+++ b/kernel/power/suspend.c
@@ -17,7 +17,6 @@
 #include <linux/console.h>
 #include <linux/cpu.h>
 #include <linux/cpuidle.h>
-#include <linux/syscalls.h>
 #include <linux/gfp.h>
 #include <linux/io.h>
 #include <linux/kernel.h>
@@ -568,13 +567,11 @@ static int enter_state(suspend_state_t state)
 	if (state == PM_SUSPEND_TO_IDLE)
 		s2idle_begin();
 
-#ifndef CONFIG_SUSPEND_SKIP_SYNC
-	trace_suspend_resume(TPS("sync_filesystems"), 0, true);
-	pr_info("Syncing filesystems ... ");
-	ksys_sync();
-	pr_cont("done.\n");
-	trace_suspend_resume(TPS("sync_filesystems"), 0, false);
-#endif
+	if (!IS_ENABLED(CONFIG_SUSPEND_SKIP_SYNC)) {
+		trace_suspend_resume(TPS("sync_filesystems"), 0, true);
+		ksys_sync_helper();
+		trace_suspend_resume(TPS("sync_filesystems"), 0, false);
+	}
 
 	pm_pr_dbg("Preparing system for sleep (%s)\n", mem_sleep_labels[state]);
 	pm_suspend_clear_flags();
diff --git a/kernel/power/user.c b/kernel/power/user.c
index 2d8b60a3c86b..68dbd9eac8e1 100644
--- a/kernel/power/user.c
+++ b/kernel/power/user.c
@@ -228,9 +228,7 @@ static long snapshot_ioctl(struct file *filp, unsigned int cmd,
 		if (data->frozen)
 			break;
 
-		printk("Syncing filesystems ... ");
-		ksys_sync();
-		printk("done.\n");
+		ksys_sync_helper();
 
 		error = freeze_processes();
 		if (error)
-- 
2.18.1