linux-kernel - [PATCH v2] PM: Use 64-bit timekeeping

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Message-ID: <20150128043836.GA4112@tinar>
Date:	Wed, 28 Jan 2015 10:08:37 +0530
From:	Tina Ruchandani <ruchandani.tina@...il.com>
To:	Linux PM List <linux-pm@...r.kernel.org>
Cc:	Arnd Bergmann <arnd@...db.de>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2] PM: Use 64-bit timekeeping

The freezer try_to_freeze_tasks uses 'struct timeval' for start
and end times, tracking time taken to freeze tasks. 'struct timeval'
on 32-bit systems will have its tv_sec overflow in year 2038 and
beyond. This patches uses 'ktime_t' (which has 64 bit values
for seconds) for start and end time.

Suggested-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Tina Ruchandani <ruchandani.tina@...il.com>
---
Changes in v2:
	- Use ktime_t to be able to use ktime_ms_delta
	  which is more efficient than timespec64 based methods.
---
 kernel/power/process.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/kernel/power/process.c b/kernel/power/process.c
index 5a6ec86..52414dd 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -17,6 +17,7 @@
 #include <linux/delay.h>
 #include <linux/workqueue.h>
 #include <linux/kmod.h>
+#include <linux/ktime.h>
 #include <trace/events/power.h>
 
 /* 
@@ -30,13 +31,12 @@ static int try_to_freeze_tasks(bool user_only)
 	unsigned long end_time;
 	unsigned int todo;
 	bool wq_busy = false;
-	struct timeval start, end;
-	u64 elapsed_msecs64;
+	ktime_t start, end;
 	unsigned int elapsed_msecs;
 	bool wakeup = false;
 	int sleep_usecs = USEC_PER_MSEC;
 
-	do_gettimeofday(&start);
+	start = ktime_get();
 
 	end_time = jiffies + msecs_to_jiffies(freeze_timeout_msecs);
 
@@ -78,10 +78,8 @@ static int try_to_freeze_tasks(bool user_only)
 			sleep_usecs *= 2;
 	}
 
-	do_gettimeofday(&end);
-	elapsed_msecs64 = timeval_to_ns(&end) - timeval_to_ns(&start);
-	do_div(elapsed_msecs64, NSEC_PER_MSEC);
-	elapsed_msecs = elapsed_msecs64;
+	end = ktime_get();
+	elapsed_msecs = (unsigned int) ktime_ms_delta(end, start);
 
 	if (todo) {
 		printk("\n");
-- 
2.2.0.rc0.207.ga3a616c

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