crc32: use ktime_get_ns() for measurement

The crc32 test function measures the elapsed time in nanoseconds, but
uses 'struct timespec' for that.  We want to remove timespec from the
kernel for y2038 compatibility, and ktime_get_ns() also helps make the
code simpler here.

It is also slightly better to use monontonic time, as we are only
interested in the time difference.

Link: http://lkml.kernel.org/r/20160617143932.3289626-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: "David S . Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/crc32.c

@@ -979,7 +979,6 @@ static int __init crc32c_test(void)
 	int i;
 	int errors = 0;
 	int bytes = 0;
-	struct timespec start, stop;
 	u64 nsec;
 	unsigned long flags;
 
@@ -999,20 +998,17 @@ static int __init crc32c_test(void)
 	local_irq_save(flags);
 	local_irq_disable();
 
-	getnstimeofday(&start);
+	nsec = ktime_get_ns();
 	for (i = 0; i < 100; i++) {
 		if (test[i].crc32c_le != __crc32c_le(test[i].crc, test_buf +
 		    test[i].start, test[i].length))
 			errors++;
 	}
-	getnstimeofday(&stop);
+	nsec = ktime_get_ns() - nsec;
 
 	local_irq_restore(flags);
 	local_irq_enable();
 
-	nsec = stop.tv_nsec - start.tv_nsec +
-		1000000000 * (stop.tv_sec - start.tv_sec);
-
 	pr_info("crc32c: CRC_LE_BITS = %d\n", CRC_LE_BITS);
 
 	if (errors)
@@ -1065,7 +1061,6 @@ static int __init crc32_test(void)
 	int i;
 	int errors = 0;
 	int bytes = 0;
-	struct timespec start, stop;
 	u64 nsec;
 	unsigned long flags;
 
@@ -1088,7 +1083,7 @@ static int __init crc32_test(void)
 	local_irq_save(flags);
 	local_irq_disable();
 
-	getnstimeofday(&start);
+	nsec = ktime_get_ns();
 	for (i = 0; i < 100; i++) {
 		if (test[i].crc_le != crc32_le(test[i].crc, test_buf +
 		    test[i].start, test[i].length))
@@ -1098,14 +1093,11 @@ static int __init crc32_test(void)
 		    test[i].start, test[i].length))
 			errors++;
 	}
-	getnstimeofday(&stop);
+	nsec = ktime_get_ns() - nsec;
 
 	local_irq_restore(flags);
 	local_irq_enable();
 
-	nsec = stop.tv_nsec - start.tv_nsec +
-		1000000000 * (stop.tv_sec - start.tv_sec);
-
 	pr_info("crc32: CRC_LE_BITS = %d, CRC_BE BITS = %d\n",
 		 CRC_LE_BITS, CRC_BE_BITS);