[PATCH] aoe: Use 64-bit timestamp in frame

[Tina Ruchandani <ruchandani.tina@gmail.com>]

'struct frame' uses two variables to store the sent timestamp - 'struct
timeval' and jiffies. jiffies is used to avoid discrepancies caused by
updates to system time. 'struct timeval' uses 32-bit representation for
seconds which will overflow in year 2038.
This patch does the following:
- Replace the use of 'struct timeval' and jiffies with ktime_t, which
is a 64-bit timestamp and is year 2038 safe.
- ktime_t provides both long range (like jiffies) and high resolution
(like timeval). Using ktime_get (monotonic time) instead of wall-clock
time prevents any discprepancies caused by updates to system time.

Signed-off-by: Tina Ruchandani <ruchandani.tina@gmail.com>
---
 drivers/block/aoe/aoe.h    |  3 +--
 drivers/block/aoe/aoecmd.c | 36 +++++++-----------------------------
 2 files changed, 8 insertions(+), 31 deletions(-)

diff --git a/drivers/block/aoe/aoe.h b/drivers/block/aoe/aoe.h
index 9220f8e..4582b3c 100644
--- a/drivers/block/aoe/aoe.h
+++ b/drivers/block/aoe/aoe.h
@@ -112,8 +112,7 @@ enum frame_flags {
 struct frame {
 	struct list_head head;
 	u32 tag;
-	struct timeval sent;	/* high-res time packet was sent */
-	u32 sent_jiffs;		/* low-res jiffies-based sent time */
+	ktime_t sent;
 	ulong waited;
 	ulong waited_total;
 	struct aoetgt *t;		/* parent target I belong to */
diff --git a/drivers/block/aoe/aoecmd.c b/drivers/block/aoe/aoecmd.c
index 422b7d8..7f78780 100644
--- a/drivers/block/aoe/aoecmd.c
+++ b/drivers/block/aoe/aoecmd.c
@@ -398,8 +398,7 @@ aoecmd_ata_rw(struct aoedev *d)
 
 	skb = skb_clone(f->skb, GFP_ATOMIC);
 	if (skb) {
-		do_gettimeofday(&f->sent);
-		f->sent_jiffs = (u32) jiffies;
+		f->sent = ktime_get();
 		__skb_queue_head_init(&queue);
 		__skb_queue_tail(&queue, skb);
 		aoenet_xmit(&queue);
@@ -489,8 +488,7 @@ resend(struct aoedev *d, struct frame *f)
 	skb = skb_clone(skb, GFP_ATOMIC);
 	if (skb == NULL)
 		return;
-	do_gettimeofday(&f->sent);
-	f->sent_jiffs = (u32) jiffies;
+	f->sent = ktime_get();
 	__skb_queue_head_init(&queue);
 	__skb_queue_tail(&queue, skb);
 	aoenet_xmit(&queue);
@@ -499,32 +497,15 @@ resend(struct aoedev *d, struct frame *f)
 static int
 tsince_hr(struct frame *f)
 {
-	struct timeval now;
+	ktime_t now;
 	int n;
 
-	do_gettimeofday(&now);
-	n = now.tv_usec - f->sent.tv_usec;
-	n += (now.tv_sec - f->sent.tv_sec) * USEC_PER_SEC;
+	now = ktime_get();
+	n = ktime_to_us(ktime_sub(now, f->sent));
 
 	if (n < 0)
 		n = -n;
 
-	/* For relatively long periods, use jiffies to avoid
-	 * discrepancies caused by updates to the system time.
-	 *
-	 * On system with HZ of 1000, 32-bits is over 49 days
-	 * worth of jiffies, or over 71 minutes worth of usecs.
-	 *
-	 * Jiffies overflow is handled by subtraction of unsigned ints:
-	 * (gdb) print (unsigned) 2 - (unsigned) 0xfffffffe
-	 * $3 = 4
-	 * (gdb)
-	 */
-	if (n > USEC_PER_SEC / 4) {
-		n = ((u32) jiffies) - f->sent_jiffs;
-		n *= USEC_PER_SEC / HZ;
-	}
-
 	return n;
 }
 
@@ -589,7 +570,6 @@ reassign_frame(struct frame *f)
 	nf->waited = 0;
 	nf->waited_total = f->waited_total;
 	nf->sent = f->sent;
-	nf->sent_jiffs = f->sent_jiffs;
 	f->skb = skb;
 
 	return nf;
@@ -633,8 +613,7 @@ probe(struct aoetgt *t)
 
 	skb = skb_clone(f->skb, GFP_ATOMIC);
 	if (skb) {
-		do_gettimeofday(&f->sent);
-		f->sent_jiffs = (u32) jiffies;
+		f->sent = ktime_get();
 		__skb_queue_head_init(&queue);
 		__skb_queue_tail(&queue, skb);
 		aoenet_xmit(&queue);
@@ -1474,8 +1453,7 @@ aoecmd_ata_id(struct aoedev *d)
 
 	skb = skb_clone(skb, GFP_ATOMIC);
 	if (skb) {
-		do_gettimeofday(&f->sent);
-		f->sent_jiffs = (u32) jiffies;
+		f->sent = ktime_get();
 	}
 
 	return skb;
-- 
2.2.0.rc0.207.ga3a616c