[PATCH v2 4/4] clock: add perf_clock posix clock

[Stephane Eranian <eranian@google.com>]

This patch is a re-packaging of David's Ahern
posix perf clock available here:

	https://github.com/dsahern/linux/blob/perf-full-monty/README.ahern

The patch itself is based on Pawel Moll's original post:

	https://lkml.org/lkml/2013/3/14/523

The new clock is call PERF_CLOCK. To use it

	#include <time.h>
	#include <linux/time.h>

	struct timespec ts;

	clock_gettime(PERF_CLOCK, &ts);

Signed-off-by: Stephane Eranian <eranian@google.com>
---
 include/uapi/linux/time.h      |  1 +
 kernel/time/Kconfig            |  6 +++++
 kernel/time/Makefile           |  1 +
 kernel/time/perf_posix_clock.c | 54 ++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 62 insertions(+)
 create mode 100644 kernel/time/perf_posix_clock.c

diff --git a/include/uapi/linux/time.h b/include/uapi/linux/time.h
index e75e1b6..9066bf0 100644
--- a/include/uapi/linux/time.h
+++ b/include/uapi/linux/time.h
@@ -56,6 +56,7 @@ struct itimerval {
 #define CLOCK_BOOTTIME_ALARM		9
 #define CLOCK_SGI_CYCLE			10	/* Hardware specific */
 #define CLOCK_TAI			11
+#define CLOCK_PERF			12
 
 #define MAX_CLOCKS			16
 #define CLOCKS_MASK			(CLOCK_REALTIME | CLOCK_MONOTONIC)
diff --git a/kernel/time/Kconfig b/kernel/time/Kconfig
index d626dc9..6e4b707 100644
--- a/kernel/time/Kconfig
+++ b/kernel/time/Kconfig
@@ -201,5 +201,11 @@ config HIGH_RES_TIMERS
 	  hardware is not capable then this option only increases
 	  the size of the kernel image.
 
+config PERF_CLOCK
+	tristate "Perf_events posix clock timer source"
+	help
+	  This option adds a new posix clock timer source which uses the same time
+	  source as the perf_events subsystem. It makes it possible to correlate
+          user level samples with perf_events samples.
 endmenu
 endif
diff --git a/kernel/time/Makefile b/kernel/time/Makefile
index f622cf2..41cd183 100644
--- a/kernel/time/Makefile
+++ b/kernel/time/Makefile
@@ -14,6 +14,7 @@ obj-$(CONFIG_TICK_ONESHOT)			+= tick-sched.o
 obj-$(CONFIG_TIMER_STATS)			+= timer_stats.o
 obj-$(CONFIG_DEBUG_FS)				+= timekeeping_debug.o
 obj-$(CONFIG_TEST_UDELAY)			+= test_udelay.o
+obj-$(CONFIG_PERF_CLOCK)			+= perf_posix_clock.o
 
 $(obj)/time.o: $(obj)/timeconst.h
 
diff --git a/kernel/time/perf_posix_clock.c b/kernel/time/perf_posix_clock.c
new file mode 100644
index 0000000..03c58b2
--- /dev/null
+++ b/kernel/time/perf_posix_clock.c
@@ -0,0 +1,54 @@
+/*
+ * Implements CLOCK_PERF.
+ *
+ * perf_clock is not exported, but for as long as I can remember perf_clock
+ * is local_clock which is exported. Make use of that.
+ *
+ * posix clock implementation by Pawel Moll
+ *     https://lkml.org/lkml/2013/3/14/523
+ *
+ * module by David Ahern, December 2013
+ */
+#include <linux/version.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/posix-timers.h>
+
+static int perf_posix_clock_getres(const clockid_t which_clock,
+	                struct timespec *tp)
+{
+	*tp = ns_to_timespec(TICK_NSEC);
+	return 0;
+}
+
+static int perf_posix_clock_get(clockid_t which_clock, struct timespec *tp)
+{
+	*tp = ns_to_timespec(local_clock());
+	return 0;
+}
+
+
+static struct k_clock perf_posix_clock = {
+	.clock_getres = perf_posix_clock_getres,
+	.clock_get = perf_posix_clock_get,
+};
+
+static int perf_posix_clock_init(void)
+{
+	/* register this character driver */
+	posix_timers_register_clock(CLOCK_PERF, &perf_posix_clock);
+
+	printk(KERN_INFO "perf_clock clock registered\n");
+
+	/* no API to unregister a clock so this module cannot be unloaded */
+	__module_get(THIS_MODULE);
+
+	return 0;
+}
+
+module_init(perf_posix_clock_init);
+
+MODULE_AUTHOR("David Ahern");
+MODULE_LICENSE("GPL");
-- 
1.9.1